METHOD AND DEVICE IN MOTOR VEHICLE BRAKES

Abstract: The invention relates to a method and a device for controlling the operating brake pressure to pressure medium brakes (18A-18D; 16A-16D) in a vehicle combination comprising a tractor vehicle and at least one trailor vehicle, said vehicles being connected by a conventional coupling device. Forces developing in said coupling device are measured during the course of braking and are reduced to a predetermined value by adjusting the brake pressure for at least the brakes (16A-16D) of said trailor vehicle in dependence of the longitudinal inclination of said tractor vehicle and of the actual deceleration thereof. The adjusted value of the brake pressure is stored so as to be the starting value at the next braking.

Description: METHOD AND DEVICE IN MOTOR VEHICLE BRAKES. The invention relates to a method and a device for controlling the operating brake pressure for pressure medium brakes in a vehicle combination com¬ prising a tractor vehicle and at least one trailer vehicle, said vehicles being connected by a conven¬ tional coupling device, according to which the driver of said tractor vehicle generates by means of a brake valve an operating pressure defining the brake pressure of said tractor and trailer vehicle, forces developing in said coupling device being measured during the course of braking and being re¬ duced to a predetermined value. The brakes of a trailer vehicle in a vehicle combination are adjusted so as to function in a satisfying way when the trailer vehicle is fully loaded. National laws and regulations stating the lowest deceleration which the vehicle combination has to fulfil when braking must also be complied with. In practice this means that certain problems arise when the trailer vehicle is uncompletely loaded or when it is not loaded at all. The problems arising are for instance wheel locking when braking, brake overheating, unnecessary wearing of the brake lining of the trailer vehicle brakes and on the coupling device between said tractor and trailer vehicle, etc. To overcome these problems it is suggested in SE 455 854 to provide in the coupling between said tractor and trailer vehicle a transducer for indi¬ cating pulling and pushing, respectively, of the coupling and that said transducer is operatively connected through a central unit to a valve for con¬ trolling the brake pressure to the brakes of said SUBSTITUTESHEET trailer vehicle. The control of the brake pressure is made through the service brake system of the tractor vehicle and is thus comparatively slow. Furthermore, the control can only take place as a decrease of the pressure existing in the tractor vehicle during the braking. An adjustment which in certain aspects is less favourable can also take place when there is a braking in a hill, and in a non-moving vehicle if there is a signal received from, the transducer while at the same time the driver presses the brake pedal. Also other problems may arise in an incorrect distribution of the braking power between the trac¬ tor and the trailer vehicle when the vehicle com¬ bination is decelerated. In a tractor vehicle having a lower braking power than accepted by law also the braking power of the vehicle combination will be un¬ satisfactory and below the accepted. If the braking ability of the brakes of the tractor vehicle is too low the result is a pushing trailer vehicle, which may result in so called jack-knifing. Said latter problem is suitably avoided by securing that the rear vehicle of the vehicle combination is braked first and that there is a certain amount of over¬ capacity in the brakes of said vehicle. Such a solu¬ tion was suggested in US 4,231,442, a device accord¬ ing to said patent comprising a power sensitive transducer arranged in the coupling between said tractor and trailer vehicle, an amplifier, and a switch connected to the brake pedal of said tractor vehicle. When the driver presses said braking pedal the brakes of the trailer vehicle are first acti¬ vated. The pulling force thereby appearing in said coupling between the vehicles actuates through said amplifier the brakes of the tractor vehicle. The amplifier is activated only if said switch has been actuated by said brake pedal. However, there is a considerable risk in activating firstly the brakes of said trailer vehicle because if said brakes do not work properly the result may be that the vehicle combination as a whole is not decelerated suffi¬ ciently neither with respect to the actual braking requirement nor with respect to the minimal de¬ celeration prescribed. To avoid wearing of the tyres and to decrease the risk of skidding there has also been suggested different systems comprising non-locking brakes. However, such systems do not overcome problems with an unnecessary wearing of the brake linings of the trailer vehicle brakes and on the coupling device between said tractor and trailer vehicle. Also, it is not possible to avoid problems with increasing differences in temperature between the different wheel brakes of the vehicle units. If the vehicles are provided with pressure brakes there is also a certain unnecessary waste of pressurized air during every course of braking because any excess pressure is ventilated so as to avoid wheel locking. However, non-locking brakes can be an excellent supplement to other types of brake control systems. An object of the present invention is to over¬ come generally the problems and drawbacks mentioned above of previously known brake control systems. .Another object of the invention is to secure a high total braking ability of the vehicle combination, to provide the required and prescribed deceleration even if any of the vehicles during operation has a problem with reduced braking ability. To this object the method and device according to the present in¬ vention have obtained the features appearing from the characterizing parts of claim 1 and 5, respect¬ ively, and from the associated sub-claims. Now the invention will be described in more de¬ tail by means of an embodiment, reference being made to the accompanying drawing, which is a schematic drawing of the device according to the invention. In the coupling between the tractor and the trailer vehicle there is provided a force sensitive transducer 10, delivering an electric signal in de¬ pendence of the force acting on said coupling. The electric signal is fed to a central unit 11 con¬ trolling in dependence of said signal and other in¬ coming electric signals the brake pressure of the air pressure brakes 16A-16D of the trailer vehicle. By means of a brake pedal, which is provided with a valve 12, said pedal being arranged in the tractor vehicle, the driver of the tractor vehicle controls the brakes 18A-18D of the tractor vehicle. Between the valve 12 and the brakes there is in a conven¬ tional way provided brake valves, said valves not being shown on the drawing for a reason of clarifi¬ cation of the invention. The primary side of said valve 12 is connected to a supply container 15, and the secondary side thereof is connected to a pressure sensitive trans¬ ducer 20 recording the so called operating pressure, and converting the pressure signal to an electric signal, which is supplied to the central unit 11. In the tractor vehicle there is provided also an ac- celerometer 13 recording the longitudinal inclina¬ tion in relation to the horizontal plane of the tractor -vehicle and also the acceleration and de¬ celeration, respectively, of the vehicle. The ac- celerometer can be of a conventional type that con¬ verts recorded signals to electric signals, which are supplied to the central unit 11. An electrically controlled valve 14 is on the primary side thereof connected to the supply con¬ tainer 15, and is operatively connected to said central unit 11, and receives from said central unit 11 an electric control signal. In dependence of said control signal the pressure supplied from said supply container 15 is adjusted to the desired oper¬ ating pressure, which is supplied to the brakes 16A-16D of the trailer vehicle through conventional coupling means between said vehicles. In accordance with the brakes of the tractor vehicle the operating pressure is utilized to actuate the brakes through conventional brake valves, not shown here. A com¬ pressor 19 maintains the desired supply pressure in said container 15. For security reasons a two-way valve 17 is provided between the valve 14 and the brakes 16A-16D of the tractor vehicle. The second input of said two-way valve 17 is supplied with operating pressure from said valve 12 of the brake. An error condition with any of the more important components of the device said two-way valve 17 is activated in such a way that the brakes of the trailer vehicle are supplied with the operating pressure of the tractor vehicle instead of the pressure adjusted to a lower value by said valve 14. This by-pass can be ac¬ complished also by means of an electric switch provided at the driver's seat. The operating pressure line from the two-way valve 17 provided on the tractor vehicle is con¬ nected to operating pressure lines on the trailer vehicle through conventional connection means 21 between the vehicles. At the driver's seat there is provided a display 22, which is operatively connected to said central unit 11, and which receives signal from said unit 11 about the present control condition and direction of forces in said coupling device between the tractor and the trailer vehicle so as to inform the driver. Any error conditions in the brakes or other relevant parts are stored in the central unit and can be read by means of indicating means that can be connected to said central unit. "0 Now a braking course on flat ground, that is, when the accelerometer at the start of the braking does not indicate any inclination, acceleration or deceleration, will be described. During driving forces in the coupling are con¬ tinuously recorded by the force sensitive transducer 10, the actual state of forces being the basis of the control. When the driver presses the brake pedal said valve 12 adjusts in relation to the pressing of the pedal the actual supply pressure to an operating pressure, which is supplied to the pressure sensi¬ tive transducer 20 and also to said two-way valve 17. The control pressure is supplied also directly to the brakes 18A-18D of the tractor vehicle. An in¬ crease of the operating pressure over a predeter¬ mined value is recorded by the central unit 11, which by a short impulse opens completely said valve 14 tfiereύby affecting the brakes of the vehicle to initiate movement towards a brake position. At the same level of the operating pressure the output of said accelerometer is also recorded. If said output indicates that the longitudinal axis of said tractor vehicle is not parallel with the horizontal plane, that is the vehicle is in a hill, or if said ac¬ celerometer indicates that the vehicle is standing still no control of the brake pressure to the brakes 35 of the trailer vehicle takes place. A previously made adjustment of the brake pressure to the brakes of the trailer vehicle instead remains during these circumstances. However, if the tractor vehicle is in a horizontal position a new control procedure as described below is initiated. If a previously made adjustment of the brake pressure exists said ad¬ justment is utilized as a initial value and a cor¬ responding pressure is supplied to the brakes through said valve 14 and said two-way valve 17. The force now acting on the coupling between the tractor and the trailer vehicle is continuously recorded by the pressure sensitive transducer 10. A pulling force indicating a brake power of the tractor vehicle which is too large is recorded by the central unit, which decreases the operating pressure through the valve 14. However, the decrease takes place only when the vehicle combination is decelerated appropriately. The deceleration is con¬ tinuously recorded by said accelerometer 13, the output thereof being processed by said central unit during the control and brake procedure. When the power acting on the coupling has been decreased to a predetermined value the control procedure is inter¬ rupted and the present value is stored in the central unit. Said value is later used as an initial value at the next brake procedure. When pushing is indicated, that is when the brake power of the trailer vehicle is too low, said central unit transmits a signal to said valve 14 to increase the operating pressure to the brakes of the trailer vehicle. As said valve 14 is supplied with supplied pressure the operating pressure to the brakes of the trailer vehicle can, if required, exceed the operating pressure to the brakes of the tractor vehicle. This is a considerable advantage because normally there are pressure losses in operating pressure lines of the tractor vehicle, said losses decreasing the available pressure inter¬ val. To achieve the prescribed deceleration higher pulling forces are allowed in the coupling even though the wear thereof is increased. However, such a control condition depends on a malfunction of the brakes of the tractor vehicle, and such a condition is stored in the central unit as described above. In respect of the present control condition of the brake pressure there is a reset of the central unit each time the driver brakes the vehicle with the parking brake. Thus, the next braking procedure is started with a non-adjusted operating pressure, that is the same control pressure to the brakes of the trailer vehicle as to the brakes of the tractor vehicle. The by-passing of said valve 14 resulting in that the operating pressure of the tractor vehicle instead is supplied to the brakes through said two-way valve 17 and may be made manually by an electric switch -not shown here. The driver has this opportunity of by-passing so as to ensure that the maximum brake pressure always can be provided to the brake of the trailer vehicle. Zero adjustment of the force sensitive trans¬ ducer and the accelerometer is made after mounting the device in the vehicle by pushing a push-button r.π switch, .the present value of the signals from said transduser and accelerometer then being stored in the central unit 11 as zero value. The zero adjust¬ ment of said transduser is then made automatically and continuously.

Claims: CLAIMS 1. Method for controlling the operating brake pressure to pressure medium brakes in a vehicle com- 5 bination, comprising a tractor vehicle and at least one trailer vehicle, said vehicles being connected by a conventional coupling device, the driver of said tractor vehicle generating by a brake valve an operating pressure determining the brake pressure on O said tractor and trailer vehicle, and forces arising in said coupling being measured during the brake procedure and being reduced to a predetermined value, c h a r a c t e r i z e d in that said operating pressure is measured and converted into an - 5 electric signal, that the longitudinal inclination of the tractor vehicle and the acceleration and de¬ celeration, respectively, of the vehicle combination are recorded, that the control of the brake pressure is started when said operating pressure exceeds a - predetermined value, said recorded longitudinal in¬ clination is below a predetermined value and said deceleration exceeds a predetermined value, and that a value of the control pressure is stored so as to be an initial value to the next brake procedure. _.. 2. Method according to claim 1, c h a r a c ¬ t e r i z e d in that the force existing during normal driving conditions in said coupling is measured, and that said measured value of the force is utilized as a preference value at continuous zero adjustments of said force sensitive transducer. 3. Method according to claim 1 or 2, c h a r ¬ a c t e r i z e d in that all braking procedures are initiated with a pressure pulse of maximum pres¬ sure to the brakes of the trailer vehicle. 35 10 4. Method according to claim 3, c h a r a c ¬ t e r i z e d in that the adjustment of the brake pressure is eliminated when the parking brake of the tractor vehicle is activated. 5. Device for controlling the brake pressure to pressure medium brakes in a vehicle combination in accordance with the method according to claim 1, said vehicle combination comprising a tractor vehicle and at least one trailer vehicle, said vehicles being connected by a conventional coupling, comprising a force sensitive transducer (10) mounted in Said coupling to measure forces arising in said coupling, a central unit (11) operatively connected to said transducer, a brake pedal valve (12) , the primary side thereof being connected to a supply container (15) , and the secondary side thereof being connected to the brakes (18A-18D) of the tractor vehicle, and an electrically controlled valve (14) , c h a r a c t e r i z e d in that converting means (20) is connected to the secondary side of said brake pedal valve (12) to record the operating pres¬ sure and to convert said pressure to an electric signal, that means (13) is provided to record the longitudinal inclination of the tractor vehicle and the acceleration and deceleration, respectively, of the vehicle combination, that the primary side of said electrically controlled valve (14) is connected to said supply container (15) , the secondary side thereof being connected to brakes (16A-16D) of the trailer vehicle, that said central unit is operat¬ C ively connected to said electrically controlled valve (14) and is constructed to start a control procedure when the operating pressure exceeds a predetermined value, when the longitudinal inclina¬ tion ' recorded is below a predetermined value, and when the deceleration exceeds a predetermined value, and that said central unit (11) is arranged to store a value of the actual brake pressure, said value being utilized as an initial value at the next braking procedure. 6. Device according to claim 5, c h a r a c ¬ t e r i z e d in that said central unit is operat¬ ively connected to a control means for the parking brake of the tractor vehicle and is arranged to reset the brake pressure to a non-controlled value when said parking brake is activated.

Inventors: HANSSON BILL, HANSSON, BILL
Applicants: VBG PROD AB, VBG PRODUKTER AB
Application year: 1990
Main classification: B60T15
IPC codes: B60T7, B60T8, B60T15