A METHOD AND AN APPARATUS FOR AUTOMATICALLY AJDUSTING THE BRAKES OF AN ARTICULATED VEHICLE PROVIDED WITH PNEUMATIC BRAKES

Abstract: A method and an apparatus for automatically adjusting the brakes of a motor-driven articulated vehicle provided with pneumatic brakes, whereby the force exerted on the traction means during braking is measured by means of a force sensor (11) coupled between a tractor vehicle (10) and a trailer (20), and the measured value is applied to a servo mechanism (12) which automatically adjusts the brakes of the articulated vehicle on the basis of the difference in the braking forces by increasing or decreasing the braking effect of the trailer.

Description: A method and an apparatus for automatically adjusting the brakes of an articulated vehicle provided with pneumatic brakes The invention relates to a method and an apparatus for automatically adjusting the brakes of a motor-driven articulated vehicle provided with pneumatic brakes, which articulated vehicle comprises a tractor vehicle or the like and a trailer coupled thereto, whereby the force exerted on the traction means during braking is measured by means of a force sensor, and the braking is adjusted on the basis of the measured value. The brakes of an articulated vehicle are usually adjusted to the value required by the maximum load mainly on the basis of theoretical calculations, decelera¬ tion measurements or dynamometer tests. However, such an adjustment is suitable for one combination and one weight ratio only. In practice it is, however, necessary to couple crosswise tractor vehicles and trailers, and since different tractor vehicles have different brake effects, the adjustment should always be carried out in connection with the coupling or when the load is changed. The influence of load changes have previously been tried to be eliminated by providing mainly the front axle of the trailer with brake valves adjustable according to the load, but these do not function properly and thus have not gained any greater popularity. The biggest drawback of prior fixed adjustments, is that in most cases the brakes of the trailer are oversized, especially when the trailer is incompletely loaded or empty. Wide variation occurs in the brake force of tractor vehicles, which leads to completely different braking properties when a trailer well suited for one tractor vehicle is coupled to another tractor vehicle. In addition, changes in the load cannot be taken into consideration in prior adjustments. Anti-locking brake systems will soon be applied to articulated vehicles, too, but this will not eliminate the need of adjustment. An additional device for such systems is disclosed in British Patent Specification 1,598,879. This device functions only if the trailer exerts an expulsive force during the braking and the adjustment only effects a reduction in the braking effect of the tractor vehicle, restricting the increase in the brake pressure of one axle or all axles. The force sensor is of the threshold value type, enabling a graded adjustment only. U.S. Patent Specification 4,231,442 discloses an apparatus which adjust the braking effect of an articu¬ lated vehicle on the basis of the braking effect of a trailer positioned last in the combination. The adjustment is carried out in the articulated vehicle in such a way that the brakes positioned at the tractor vehicle end of the combination are the last ones to be adjusted. At first only the rear wheels are activated by the brake pedal and thereafter the braking effect of the tractor vehicle is adjusted on the basis of the force . of the drawbar so that it corresponds to the braking effect of the trailer. A traction force has to exist between the carriages of the articulated vehicle in order that the apparatus would adjust the brakes of a carriage positioned in front of another part. If the brakes of the carriage positioned last in the combination do not function for one reason or another, no traction force is created in the drawbars, as a result of which the system does not function. Also in this system the total decelaration is determined on the basis of the braking effect of the trailer. Both these known systems are very complicated and they cannot be installed afterwards. They are not acceptable in general use, since they reduce the decelera¬ tion of the tractor vehicle, so that the combination does not fulfil the requirements of e.g. the Finnish legislation on vehicles, which requires a deceleration 2 of 5 m/s with a pressure of 450 kPa. With the permissible weight ratios, it is possible to adjust only the braking effect of the trailers in order to maintain the required deceleration, since in most cases the trailer is empty or incompletely loaded, whereas the tractor vehicle has a full load. On the other hand, when the whole combination is full or respectively empty, the weight ratio between the tractor vehicle and the trailer is changed to such an extent (22/26 -10/6) that when there is not load at all, the brakes of the trailer are considerably oversized in relation to the brakes of the tractor vehicle. The components in the apparatus according to the invention are similar to those used in known apparatuses, whereas the principle of adjustment and the realization are completely different: - the force measurement is linear and is carried out continuously in both directions, - the adjustment affects only the braking effect of the trailer as it changes the control pressure so that the tractor vehicle determines the maximum deceleration to be obtained without any risk of the trailer skidding, - the entire apparatus can be easily placed in the tractor vehicle. The object of the method and the apparatus accord¬ ing to the invention is to provide a decisive improve¬ ment in the aforementioned disadvantages. For the achievement of this object, the method according to the invention is characterized in that both traction force and pushing force are measured by means of the force sensor, the need for adjustment being determined on the basis of the direction and magnitude of the force by means of a logic which gives an instruc¬ tion which effects either a reduction or respectively an increase in the braking effect of the trailer. The apparatus according to the invention comprises a force sensor positioned between the parts of the arti¬ culated vehicle, a servo control unit and a control pressure regulator, and it is characterized in that the force sensor measures both traction and pushing force and is connected to the servo control unit, which comprises a comparator which detects from an impulse applied from the force sensor whether the force acting between the tractor vehicle and the trailer of the articulated vehicle is a pushing force or a traction force, said comparator controlling an amplifier of the servo control unit, which amplifier controls the air pressure of the brakes of the trailer through the control pressure regulator. The force sensor is preferable positioned in the draw coupling or in the drawbar. As compared to known solutions, the invention has e.g. the following advantages: - the adjustment affect the trailer only so that the above deceleration requirement is met under all conditions, - changes in the load of both parts of the combination can be taken into consideration according to the invention. The force of the drawbar is determined by means of the following equation: x m - F _i ' ■ __. i J l x m. F = — , in which m l + m 2 Fa = the draw-bar force (N) F ... = the summation (total) brake force of the traction vehicle (N) . = tthhee ssuummmmaattiioonn ((ttoottaal) brake force of the trailer vehicle (N) ir = the mass of the traction vehicle (kg) rr = the mass of the trailer (kg) - the entire apparatus is preferably mounted in the tractor vehicle although the adjustment affects only the trailer, which is an advantage in that one and the same tractor vehicle can be used with trailers of various types and braking effects without changing the braking system of the trailers. This is very practi- cal, because it is very common to use one and the same tractor vehicle with different trailers, - it might be possible to mount the apparatus wholly in the trailer, in which case the tractor vehicle, correspondingly, would not require any additional means; however, this application is not as practical as the preceding one, - the apparatus replaces a prior manually operated adjusting valve and so-called load-sensitive (ALB) valves (in the tractor vehicle and the trailer) , - the apparatus can be easily constructed portable so taht it can be displaced from one vehicle to another, - the apparatus does not risk the normal opera¬ tion of the brakes in case of failure, - when the allowance for adjustment of the brakes is not possible due to excessive wear the driver is informed of failure and the need of the repair of the brakes, - the apparatus does not require any changes in existing brakes and coupling means. The road safety is increased substantially, because it is possible by means of the apparatus according to the invention to prevent the trailer from tossing from side to side especially when the brakes are applied in sudden situations. in the following the invention will be described by means of one embodiment with reference to the attached drawing, wherein Figure 1 shows generally the positioning of the apparatus in an articulated vehicle, Figure 2 shows a preferred position of the force sensor of the apparatus, and Figure 3 illustrates schematically the operation of the apparatus. According to Figure 1 and 2, a force sensor 11 is placed in the coupling between a tractor vehicle 10 and a trailer 20, which sensor is preferably an electrical strain gauge. As shown in Figure 2, the force sensor 11 is fitted in the draw coupling of the tractor vehicle 10 in such a way that itis positioned between a fastening nut 21 thereof and that end 29 of the draw coupling which faces towards the trailer 20 and that said fastening nut 21 is positioned on one side of the force sensor 11 and a steel plate 22 is positioned on the other side thereof, the steel plate being followed, in the dircetion towards the draw-coupling end 29 facing the trailer 20, by a rubber plate 23, a steel plate 24, a draw plate 25 of the body of the tractor vehicle 10, a steel plate 26, a rubber plate 27, a steel plate 28 after which said end 29 is positioned. Due to the rubber plates 23 and 27, the force sensor 11 is squeezed between the f stening screw 21 and the steel plate 22, which squeezing is compensated by setting the apparatus to zero. The deformation of the rubber plate 23 and 28 in long-term use is compensated similarly. The force sensor 11 is connected to a servo control unit 12 from which a display and failure message is applied to a display device 14 positioned in the cabin. The servo control unit 12 communicates with a control pressure regulator 13 through a cable 15. According to Figure 3 the force sensor 11 is electrically connected to a comparator 16 of the servo mechanism. If a traction load is exerted on the traction means, i.e. the force sensor 11, during braking, that is, if the brakes of the trailer are oversized, the comparator 16 detects this minus-sign voltage and gives an amplifier 17 an instruction to reduce the control pressure to such an extent that the traction load is eliminated so that the voltage from the sensor goes to zero. The amplifier 17 gives said instruction e.g. to an actuating means 18, which can be a cylinder, a motor or the like, or gives said instruction directly without passing any actuating means to a pressure regulator 13 which is connected in such a manner that it adjusts the control pressure of the brakes of the trailer. The comparator 16 obtains a continuous operating voltage from the electrical system of the vehicle, whereas the amplifier 17 obtains a voltage only during braking, e.g. from a brake light switch 19. When a pushing force is exerted on the traction means, the comparator 16 detects a plus-sign voltage and the control pressure is increased until the voltage supplied by the sensor 11 is zero. The pressure regulator 13 functions only during braking, because it obtains operating voltage from the brake light switch 19. The adjustment of the brakes is thus always carried out after the coupling in connection with the first application of brakes and always during the first application of brakes after the load of the vehicle is changed, the fine adjustment being carried out in connection with each application of the brakes. For security reasons magnetic valves 30 and 31 are attached to the control pressure regulator 13 both on the inlet and the delivery side of the pressure air. The magnetic valves 30, 31 enable the shunting of the pressure regulator 13 if an electrical failure occurs in the control system, if the parking brake is on or when applying a manually operated trailer brake, a so-called emergency brake; that is, the shunting is needed in sudden situations when it must be ascertained that the trailer will be braked. A pressure air conduit leading to the pressure regulator 13 is indicated by the reference numeral 32 and a pressure air conduit from the regulator by the reference numeral 32. The reference numeral 33 designates the coupling connection to the trailer brakes. The apparatus further comprises a display device 14 positioned in e.g. the cabin of the tractor vehicle 10 for observing the operation and for indicating a need of service. The logic means also obtain data from the back light switch 19, which ensures that the adjustment is carried out in the right direction during reversing, too.

Claims: Claims : 1. A method for automatically adjusting the brakes of a motor-driven articulated vehicle provided with pneumatic brakes, which articulated vehicle comprises a tractor vehicle or the like and a trailer coupled thereto, wherein the force exerted on the traction means during braking is measured by means of a force sensor connected between the carriages of the articulated vehicle and the brakes of the articulated vehicle are adjusted on the basis of the measured value, c h a r a c ¬ t e r i z e d in that both traction force and pushing force are measured by means of the force sensor (11), the need for adjustment being determined on the basis of the direction and magnitude of the force by means of a logic which gives an instruction which effects either a reduction or respectively an increase in the braking effect of the trailer (20) . 2. An apparatus for automatically adjusting the brakes of a motor-driven articulated vehicle, comprising a force sensor connected between the carriages of the articulated vehicle, a servo control unit and a control pressure regulator, c h a r a c t e r i z e d in that the force sensor (11) measures both traction and pushing force and is connected to the servo control unit (12),which comprises a comparator (16) which detects from an impulse applied from the force sensor whether the force acting between the tractor vehicle (10) and the trailer (20) of the articulated vehicle is a pushing force or a traction force, said comparator controlling an amplifier (17) of the servo control unit, which amplifier controls the air pressure of the brakes of the trailer (20) through the control pressure regulator (13). 3. An apparatus according to claim 2, c h a r a c - t e r i z e d in that the pressure regulator (13) is connected to the brake circuit of the tractor vehicle (10) so that it obtains an operating voltage from a brake light switch (19) only during braking. 4. An apparatus according to claim 3, c h a r a c ¬ t e r i z e d in that three-way magnetic valves (30, 31) are attached to the control pressure regulator (13) both on the inlet and the outlet side of the pressure air, which valves enable the pressure regulator (13) to be shunted if there is an electrical failure in the control system, if the parking brake is on, or when applying a manually operated trailer brake, i.e. an emergency brake. 5. An apparatus according to any of the claims 2 to 4, c h a r a c t e r i z e d in that it comprises a display device (14) which is arranged to be fitted in the cabin of the tractor vehicle (10) and which is connected to the output of the comparator (16) , which display device enables the braking to be controlled and indicates a possible need of services of the brakes. 6. An apparatus according to any of the claims 2 to 5, c h a r a c t e r i z e d in that the force sensor (11) is an electrical strain gauge (11) . 7. An apparatus according to claim 6, c h a r a c ¬ t e r i z e d in that the strain gauge (11) is fitted in the draw coupling of the tractor vehicle between the fastening nut (21) of the coupling and that end (29) of the draw coupling which faces towards the trailer (20) . 8. An apparatus acccording to any of the claims 2 to 7, c h a r a c t e r i z e d in that all the com¬ ponents (13, 16, 17, 18) of the apparatus, with the exception of the force sensor (11) , are so enclosed that they are easy to position in the tractor vehicle (10) afterwards as an auxiliary, for instance.

Inventors: SARAMO JORMA, SARAMO, JORMA
Applicants: SARAMO JORMA, SARAMO, JORMA
Application year: 1987
Main classification: B60T7
IPC codes: B60T7, B60T13, B60T17