METHOD AND ARRANGEMENT FOR BRAKE ADAPTATION BETWEEN A HAULAGE VEHICLE AND AN ATTACHED SEMITRAILER

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 by means 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. The adaptation means that the brakes of the haulage truck (1) and of the semitrailer (2) can be used better under various operating conditions.

Description: Method and arrangement for brake adaptation between a haulaσe vehicle and an attached semitrailer The invention relates to an arrangement and a method for brake adaptation in accordance with the preamble of attached Patent Claims 1 and 8. Prior art In relatively heavy vehicle combinations an adaptation must be made between the braking systems of a haulage vehicle and an attached semitrailer. In this connection the principal aim is to let each wheel axle be responsible for the braking of the load which rests on the respective axle in order to obtain as uniform a load as possible on the brakes of the respective wheels. Should one brake absorb too great a share of the total braking work, this results in the brakes being overloaded and being worn abnormally quickly. If, on the other hand, the brakes are underloaded, this results in an unneces¬ sarily long braking distance. The laws and regulations which determine the braking characteristics of vehicles permit a certain difference to exist between different vehicle parts. In cases where the haulage truck and semitrailer have different braking characteristics this can result, when there is relatively low brake pressure, in only the brakes of the haulage vehicle being applied and thereby having to brake the entire vehicle unit. This disadvan¬ tage can be further aggravated for example in older semitrailers, where the brakes can often seize on account of corrosion and poor maintenance. Very few braking operations normally take place with fully applied brakes. Instead, the majority of braking operations take place with low or moderate brake pressure, with the result that the problem discussed above manifests itself. As a result of this the brake linings of the haulage truck are loaded to an unnecessary extent, and they are consequently worn out quickly and therefore have to be frequently changed. Another point of interest is that, in the case of a semitrailer, part of its load is absorbed by the wheels of the haulage truck and another part by the wheels of the semitrailer. As already mentioned, the principal aim is that each wheel should be responsible for the braking work which is required for the mass resting on the respective wheel. This means that, depending on how the semitrailer is loaded, the haulage truck must absorb different degrees of braking work. There is at present no satisfactory solution to the problem described. There are certain types of control valves for the brakes of the semitrailer, which valves allow the pressure imparted to the brakes of the semi¬ trailer to be manually adjusted, within certain limits, relative to the pressure imparted to the brakes of the haulage truck. However, such an adjustment requires comprehensive measuring equipment, and even when adjust- ment is carried out for a particular semitrailer it is not certain that the same adjustment is suitable for another semitrailer. This adjustment can also only be made for a specific load and, in the event of reloading or another freight, the conditions for the adjustment are altered. All these disadvantages of manual adjustment have meant that a single adjustment is made once only which is suitable for the most general driving condi¬ tions, and no further adjustment is then made. In the case of a trailer, which unlike a semi- trailer completely supports its own load, it is known to arrange force sensors which, during braking sequences, detect the force acting on its drawbar. If, during a braking sequence, a tensile force is detected acting on the drawbar, this is an indication that the brakes of the trailer are responsible for too large a proportion of the braking work. Correspondingly, a compressive force on the drawbar indicates that the brakes of the trailer are responsible for too small a proportion of the braking work. Depending on these indications a control valve for the brakes of the trailer is actuated so as to increase or decrease the brake pressure imparted to the brakes of the trailer. This technique cannot however be directly transferred to a semitrailer, since in this case a certain proportion of the load of the semitrailer is to be braked by the brakes of the haulage vehicle. Object of the invention The object of the present invention is to solve the problem discussed and thus to provide a brake adap- tation of the braking system of the semitrailer as a function of the braking system of the haulage truck. By this means their respective braking systems can be better used. One object of the invention is that this adaptation should take place automatically and should be able to be carried out individually for the specific semitrailer which at the time is attached to the haulage truck. When the semitrailers are changed, an automatic adaptation shall take place with regard to the new semitrailer. The invention relates both to an arrangement for carrying out the brake adaptation in accordance with what is stated in the characterizing part of Patent Claim 1, and also a method according to Patent Claim 8. The invention results in the haulage truck and semitrailer each being responsible for a braking work corresponding to the axle pressure borne by the respec¬ tive axle to an essentially better extent than is the case in the known solutions. This means that the brake linings are loaded and worn more evenly. The invention also results in it being possible for the same haulage truck to be used together with different semitrailers, whose braking systems have different braking properties, in which connection the advantages of the invention are obtained regardless of which semitrailer is chosen. Further features and advantages characterizing the invention will emerge from the attached illustrative description of an advantageous embodiment. Brief description of the drawings The illustrative description is given with reference to the attached drawings in which Figure 1 shows a haulage truck with attached semi¬ trailer, with various components in their respective braking systems being shown diagrammatically. Figure 2 shows a diagram of the individual deceleration of the haulage truck and the semitrailer at different brake pressures and in a non-adapted condition, and Figure 3 shows a corresponding diagram after brake adaptation has been carried out. Description of an exemplary embodiment Attached Figure 1 shows diagrammatically a vehicle consisting of a haulage truck 1 and an attached semitrailer 2. The haulage truck 1 and the semitrailer 2 are equipped with pneumatic brake systems, which are conventional per se, for activation of brake members on each wheel. However, since the design of such pneumatic brake systems is well known in connection with at least relatively heavy vehicles, the following description is limited to including only those parts which are of importance for describing the present invention. For the purpose of simplifying the description, simplified brake systems are therefore exemplified. The brake system of the haulage truck 1 comprises a compressed air source 5 in the form of a compressor. This is connected via a supply line 6 to, on the one hand, a relay valve 7 of the brake member 3 on the rear wheel of the haulage truck emd, on the other hand, to a control valve 8 for the semitrailer 2, generally called the control valve of the trailer. Both these valves 7, 8 are connected via an operating pressure line 9 to a brake control valve 10, which is controlled by means of a brake pedal which can. be actuated by the vehicle driver. The brake control valve 10 is also supplied with compressed air from the compressed air source 5 and, depending on the position of the brake control valve 10, the operating pressure line 9 is supplied with a certain brake pressure Pb. The brake system of the semitrailer 2 similarly comprises a supply line 11 and an operating pressure line 12 connected to a relay valve 13 on the brake member 4 on the wheel of the semitrailer. The supply line 11 is connected to the supply line 6 of the haulage truck 1 and the operating pressure line 12 is connected to the control valve 8 of the haulage truck 1 for the semi¬ trailer 2. The operating pressure line 12 and supply line 11 of the semitrailer 2 comprise coupling pieces which connect the brake system of the semitrailer 2 to the brake system of the haulage truck 1. The coupling pieces are shown diagrammatically in Figure 1 as a coupling block 14. The figure shows the coupling block 12 in a displaced position. In practice the coupling block 12 is positioned in a suitable space between the haulage vehicle 1 and the semitrailer 2. The control valve 8 for the semitrailer 2 is designed to emit, depending on the operating pressure Pb which is emitted by the brake control valve 10, an operating pressure for the semi- trailer 2, which operating pressure can be higher than, lower than or equal to the operating pressure Pb of the haulage truck. The control valve 8 comprises a control member 15 for controlling the operating pressure of the semitrailer 2 as a function of the operating pressure of the haulage truck. This control thus means that the braking work can be divided between the brake members 3, 4 of the haulage truck 1 and the semitrailer 2. In accordance with the present invention the brake system of the haulage truck 1 also comprises an electrical control unit 16 which is connected to a number of sensors detecting different vehicle parameters. In this example the control unit 16 is connected to an electrical pressure sensor 17 in the operating pressure line 9 of the haulage truck 1. The control unit 16 is thereby supplied with a signal representing the brake pressure Pb of the haulage truck 1, which pressure is in itself dependent on the activation of the driver-actuated brake control valve 10. This signal can therefore also be regarded as representing a braking capacity desired by the driver. The control unit 16 is also connected to a deceleration sensor 18, which in Figure 1 is only shown diagrammatically. In practice the deceleration sensor 18 can be made up of a sensor which, during a time sequence. detects the speed of rotation of at least one of the wheels of the vehicle and whose signal is converted by means of conventional signal processing to represent the deceleration. In an alternative embodiment the deceleration sensor 18 can be made up of a pendulum sensor, whose swing amplitude is directly proportional to the decelera¬ tion. A pendulum sensor has the advantage of automatical¬ ly adapting its output signal with regard to the inclina- tion of the vehicle when the latter is on a slope. Such a pendulum sensor can therefore also be used together with a deceleration sensor of the above entioned design, detecting the wheel speed in order to compensate the signal representing the deceleration with regard to the inclination of the vehicle. A third sensor 19 is connected to the control unit 16, which sensor 19 detects the load on the rear axle of the haulage truck 1. Provided that the haulage truck 1 is equipped with air suspension, this sensor 19 can in practice be made up of a pressure sensor arranged in the compressed air bellows of the spring suspension, as shown in Figure 1. Should the haulage truck 1 not have such a spring suspension, another conventional sensor can be arranged to detect the axle load for the rear wheels of the haulage truck 1. The said three sensors 17, 18, 19 are thus designed to detect and supply the control unit 16 with signals representing the said vehicle parameters. The control unit 16 comprises a memory unit 20 and a comparative circuit 21. In the memory unit 20 various predetermined values are programmed in for the expected deceleration of the vehicle as a function of the brake pressure Pb of the haulage truck 1 and the axle load of the rear wheels of the haulage truck 1. The sensors 17, 19 detecting these two vehicle parameters are connected to the memory unit 20 and emit, as a function thereof, an output signal representing an expected deceleration under the actual conditions. This output signal is supplied to the comparative circuit 21, to which there is also supplied a signal from the decelera¬ tion sensor 18 detecting the actual deceleration. The comparative circuit 21 compares these signals and emits an output signal representing the discrepancy. The comparative member 21 of the control unit 16 is electri¬ cally connected to the control member 15 for the control valve 8 for the semitrailer 2. The control member 15 can be made up, for example, of an electrical stepping motor which mechanically influences the control valve to change its position such that the operating pressure which is emitted to the operating pressure line 12 of the semi¬ trailer 2 is modified as a function thereof. In an alternative embodiment the control member 15 can be made up of an electrically activatable pneuma- tic proportional valve, the position of the control valve 8 being modified pneumatically. The function of the described arrangement is as follows. It is assumed that the haulage truck 1 and the semitrailer 2 have recently been connected to each other and that their respective brake systems have not been adapted to each other. Figure 2 shows the character of the individual deceleration R of the haulage truck 1 and semitrailer 2 for different brake pressures Pb in the operating pressure line 9 of the haulage truck 1. The line A represents the deceleration of the haulage truck and the line B the deceleration of the semitrailer. The deceleration of the whole vehicle combination corresponds to a mean (not shown) of these two curves in proportion to the respective weight of the haulage truck and the semitrailer. Thus, if the haulage truck 1 and the semi¬ trailer 2 have the same weight, the mean of the curves will lie exactly midway between the two curves A and B shown. If, on the other hand, one of the vehicle parts 1, 2 has a greater part of the total weight of the vehicle combination than the other vehicle part, the curve for the mean will correspondingly lie closer to that one of curves A and B which corresponds to the heavier of the vehicle parts 1, 2. As emerges from the line B in Figure 2, the brakes of the semitrailer 2 start to be applied at a considerably higher brake pressure Pb2 than the brakes of the haulage truck 1. At low brake pressures up to Pb2 the brakes of the semitrailer 2 do not effect any braking work. The fact that the brakes of the semitrailer 2 exhibit this characteristic may be due to its brake system being mechanically more power-consuming, for example on account of rust formation or because it is unlubricated. Regardless of the reason, it is desirable in this case to increase the operating pressure which is imparted to the operating pressure line 12 of the semi¬ trailer. When the vehicle combination is decelerated, there arises in the operating pressure line 9 of the haulage truck 1 a brake pressure Pb which, in accordance with Figure 2, applies the brakes. The pressure sensor 17 in the operating pressure line 9 and the load sensor 19 emit to the memory unit 20 of the control unit 16 signal values representing these vehicle parameters. The memory unit 20 thereby emits a signal representing an expected deceleration, which signal is compared in the comparative circuit 21 to a signal representing the actual decelera¬ tion from the deceleration sensor 18. In this case the share of the braking work effected by the semitrailer 2 is small if anything, and as a result of this the actual deceleration is lower than the expected deceleration. The comparative circuit 21 therefore emits an output signal which indicates that the operating pressure to the semitrailer 2 should be increased. However, this adjust¬ ment does not take place until the braking sequence is complete. In order for the control system 16 to be able to detect that a braking sequence is complete, a detec¬ tion member intended for this purpose is provided (not shown) . This detection member can advantageously be combined with the pressure sensor 17 for the brake pressure of the haulage truck. If the brake pressure is zero, this is an indication that a braking sequence is complete. When the actual braking sequence has been completed, the output signal from the control unit 16 to the control member 15 of the control valve 8 influences its position so that it results in the operating pressure to the semitrailer being increased before the next deceleration. This adjustment can take place either with a certain predetermined step, for example 0.1 bar, for each deceleration or with a complete adjustment, cor¬ responding directly to the discrepancy noted in the comparative circuit 21, for each deceleration. Assuming that the adjustment takes place stepwise, then after a number of decelerations the brakes of the haulage truck and the semitrailer come to be adapted to each other. Attached Figure 3 shows the character of the deceleration R of the semitrailer and the haulage truck as a function of the brake pressure Pb after their brakes have been adapted to each other in the abovementioned manner. The brakes of the haulage truck 1 exhibit, according to line A, the same characteristics as in Figure 2, while, on the other hand, the brakes of the semitrailer 2 according to line B have been moved paral¬ lel relative to what is shown in Figure 2. This adjust- ment applies primarily to a certain specific brake pressure Pbl. It is unlikely that a subsequent decelera¬ tion will take place with the same brake pressure. If the brake pressure upon a subsequent deceleration is lower than this pressure Pbl, an excessive deceleration will be detected in analogy with what has been described above. This is an indication that the brakes of the semitrailer 2 are performing an excessive braking work for the actual brake pressure Pb. The control unit 16 therefore effects an adjustment which results in the operating pressure to the semitrailer being decreased relative to the operating pressure to the brakes of the haulage truck. In an analogous manner the operating pressure to the semi¬ trailer increases if the braking is effected with a pressure exceeding Pbl. The control unit in this way continuously and automatically adapts the brake systems of the haulage truck and the semitrailer to each other. Should, for example, the load of the semitrailer be significantly altered, this will result in other condi¬ tions which alter the expected deceleration, adaptation being effected in accordance with these new conditions. The adaptation is most urgent in the case of relatively low brake pressures, since the majority of decelerations are effected with low brake pressures. The adaptation described is therefore intended primarily to take place when the brake pressure is less than a pre¬ determined pressure, which is advantageously of the order of magnitude of 2 bar. A conventional pneumatic com¬ pressed air brake system normally operates with pressures up to about 7 bar. The stated limit under which adjust¬ ment is carried out thus corresponds to about 30% of the maximum existing pressure. In the case of braking with higher brake pressures, no adjustment need therefore take place which affects the position of the relay valve. Despite the fact that two consecutive decelerations do not take place with exactly the same brake pressure Pb, the discrepancy between the two curves is extremely small, or at least much less than when no brake adjust¬ ment is carried out. As a result of this the individual decelerations of the haulage truck 1 and the semitrailer 2 are nevertheless sufficiently similar to each other for a' satisfactory distribution of the braking work to be obtained. In a more developed variant of the invention the control unit is supplied with further vehicle parameters of significance for the adjustment. Among these para¬ meters there may be mentioned the motor speed of the drive motor of the haulage truck in order to indicate the motor brake function. If motor brake function is present, the drive wheels perform a certain braking work which in other cases is not noted. This would result: in false information being supplied to the control unit regarding the braking work which is actually carried out. The same applies when the vehicle is equipped with an additional brake, a so-called retarder, in which connection the control unit should be supplied with a signal which indicates when it is activated. If the vehicle is equip¬ ped with an automatic brake control system (ABS), the control unit should likewise be supplied with a signal which indicates when it is activated. These signals can be used to modify or adapt the control unit's adjustment of the control valve of the semitrailer. In this context it should be noted that the invention is particularly advantageous in a vehicle equipped with an automatic brake control system (ABS) . Such a system ensures that none of the wheels of the vehicle are locked, which means that the brake adaptation can be carried out without regard to the risk of wheels locking. In the example described, which shows a simpli¬ fied braking system, nothing has been said of the brake members on the front wheels of the haulage truck. Brake members which are conventional per se are advantageously arranged on these. The invention can be further modified within the scope of the attached patent claims and can be designed other than has been stated in the example described. The invention is not limited to purely pneumatic brake systems, but can also be used, for example, in electro- pneumatic brake systems. In such a case the control member of the control valve can be made up of an electri¬ cal circuit which effects the control by means of suit¬ able signal processing. No mechanical or pneumatic control of the same valve is thus required if this is electrically operated, as is customary in electropneuma- tic brake systems.

Claims: CLAIMS 1. Arrangement for brake adaptation between a haulage vehicle (1) and an attached semitrailer (2) comprising a control valve (8) for controlling the brake pressure imparted to the semitrailer (2) as a function of the brake pressure of the haulage vehicle (1), the control valve (8) being connected to a control member (15) by means of which the brake pressure imparted to the semitrailer (2) can be varied relative to the brake pressure of the haulage vehicle (1), characterized in that the control member (15) is electrically connected to and can be actuated by an electrical control unit (16) comprising a memory unit (20) and a comparative circuit (21) cooperating therewith, in that the memory unit (20) contains stored values for an expected deceleration as a function of vehicle parameters for the haulage vehicle (1), in that the control unit (16) is electrically connected to sensors (17, 19) for detecting these vehicle parameters and to a sensor (18) for detecting the actual deceleration of the vehicle during a braking sequence, and in that the comparative member (21) is designed to compare signal values representing the actual decelera¬ tion with the deceleration corresponding to the detected vehicle parameters, and, in the event of a discrepancy between these, the control unit (16) controls the posi¬ tion of the control member (15) and thus of the control valve (8) such that the semitrailer (2) is supplied with a lower or a higher brake pressure as a function of the discrepancy. 2. Arrangement according to Claim 1, characterized in that the detected vehicle parameters are made up at least of the brake pressure of the haulage vehicle (1) and the load which rests on the haulage vehicle (1). 3. Arrangement according to Claim 2, characterized in that the vehicle parameters are made up of the brake pressure imparted to the brake member (3) of the rear wheels of the haulage truck (1) and the load which rests on the rear wheels of the haulage vehicle (1). 4. Arrangement according to Claim 2, characterized in that the control unit (16) is designed to carry out the control of the control member (15) after a completed braking sequence. 5. Arrangement according to Claim 2, characterized in that the control of the control member (15) is only carried out when the brake pressure of the haulage truck (1) is below a certain predetermined value. 6. Arrangement according to Claim 2, characterized in that the control of the control member (15) is carried out stepwise with a predetermined value at each control, with the result that the brake pressure imparted to the semitrailer (2) is modified on each control by a pre¬ determined value. 7. Arrangement according to Claim 6, characterized in that the control of the control member (15) is carried out only when the brake pressure of the haulage truck (1) is below about 30% of the maximum existing brake pres¬ sure. 8. Method for carrying out brake adaptation between a haulage vehicle (1) and an attached semitrailer (2), in which connection a control valve (8) is designed to control the brake pressure which is imparted to the semitrailer (2) as a function of the brake pressure of the haulage vehicle (1) and as a function of the position of a control member (15) for the control valve (8) , characterized in that the brake pressure of the haulage vehicle (1) and the load of the haulage vehicle are detected and signals representing these parameters are supplied to a control unit (16) comprising a memory unit (20) in order to take from it a signal representing an expected deceleration, in that the actual deceleration of the vehicle (1) is detected and a signal representing the actual deceleration is supplied to the control unit (16) and is compared with the signal representing the expected deceleration, and in that the control unit (16), in the event of a discrepancy between the expected and actual deceleration, emits an output signal to the control member (15) for the control valve (18) in order to modify the brake pressure imparted to the semitrailer (2) in proportion to the brake pressure which has been detected in the haulage vehicle (1).

Inventors: FREDRIKSSON ROLF, GARDELL LARS, MAGNUSSON GOERAN, FREDRIKSSON, ROLF, GARDELL, LARS, MAGNUSSON, GOERAN
Applicants: SAAB SCANIA AB, SAAB-SCANIA AKTIEBOLAG
Application year: 1989
Main classification: B60T7
IPC codes: B60T7, B60T8, B60T13