GB1587405A

GB1587405A - Braking systems

Info

Publication number: GB1587405A
Application number: GB2712576A
Authority: GB
Original assignee: DILLTOWN HOLDINGS Ltd
Current assignee: DILLTOWN HOLDINGS Ltd
Priority date: 1977-07-18
Filing date: 1977-07-18
Publication date: 1981-04-01

Description

(54) BRAKING SYSTEMS: We, We, DILLTOWN HOLDINGS LIMI TED, a British Company of 3 The Martins Drive, Leighton Buzzard, Bedfordshire, LU7 7TQ, do hereby declare that the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed,. to be particularly described in and.

by the following statement This invention. relates to braking systems for towed vehicles and is particularly, but not exclusively,. concerned with braking systems for agricultural trailers The braking systems of agricultural trailers in. common use. at present provide that braking of the trailer is effected by manual means, with the. result that the braking system of the trailer is usually used only when parking the trailer. Whilst being towed the trailer relies on the braking provided by the towing vehicle or tractor.

With increasing trailer loads and the use of sealed cabs on agricuItural tractors (for safety and noise abatement). new trailer braking systems are required. Proposals have been made both in the U.K. and Europe that the standards of the braking systems used in trailers be improved, and. the present invention aims to provide a system which might be used with a minimum of modification to the towing vehicle.

According to the invention a braking system for a towed vehicle, comprises a fluid pressure generator operable' to. displace fluid from a reservoir into a distribution network having passage means communicating with one or more brake actuation chambers and a return branch to the reservoir, and contol means for controlling operation of the fluid pressure generator to regulate the rate at which fluid is. displaced thereby and thus control the braking force applied. to the towed vehicle,. said control means being re responsive, when the towed vehicle, is. connected to a towing vehicle, to. an. electrical signal indicative of a desired rate of braking of said towing vehicle.

The trailer' braking system may with advan tage include means responsive to movement of the towed vehicle to produce at least part of the power needed to stop the towed vehicle when the brakes of the towing vehicle are applied.

Embodiments of the invention applied to agricultural tractor-trailer braking systems will now be described with reference to the accompanying drawings in which: Figure- 1 is a schematic diagram' of one form of an hydraulic braking system used in an agricultural tractor; and Figure 2 diagrammatically shows three modes. of braking obtainable. with the system of Figure 1.

Figure 3 is a schematic diagram of part of an alternative to the- system. of Figure 1.

A. hydraulic braking system: of arl agricul tural trailer is. shown generally at A,' the.

electrical connection from it to the electrical system of a tractor towing the trailer shown partially at B, are made in the usual way with plugisocket connections.

The hydraulic braking system of the trailer is controlled via a control box 10 which controls energisation of a D..C. electric. motor 11. The control box 10 is connected. in an electrical circuit with the motor 11 via a switch 12 which is normally biased open (for example, by means; of a spring, not shown) and which is closed when a solenoid }3, connected in the circuit of the trailer stop' lamp 14, is energized by depression of' the tractor brake pedal (shown. diagrammatically at 15).

Motor 11 drives a hydraulic pump 16 to energise an hydraulic circuit including the brake pistons of each brake of the trailer (only one of these brake pistons, 17, being shown) The pump 16 pumps hydraulic fluidj frorn a reservoir 18. via a hydraulic network including pipe 19 to the brake pistons 117 The hydraulic pipe 19 is coupled to a return branch 20 including a mechanical throttle valve 21 and a normally open' electrieally operable valve 22.

Energisation of motor 11, and therefore its speed and the speed of the. pump 16,. is controlled by the control' box 10 in a manner which will now be described, Upon depression of the brake pedal E5 a wiper arm P attached to the end thereof moves to contact a conductor 23 connected as shown to the tractor battery 24 and energises the stop light 14 of the trailer and the solenoid operated switch 13 resulting in the closure of the electrical circuit including the control box 10. Wiper arm P also moves across the first sector a of a rheostat 25 and energises the control box to drive the motor 11 at a chosen speed, Nl, some 25% of its maximum chosen speed (see Figure 2).

Hydraulic fluid pumped by the pump 16 from the reservoir 18 to the pipe 19 is diverted at least in part via the manual valve 21 and normally open valve 22 back to the reservoir 18. The braking force applied to the brake pistons 17 is therefore less than the maximum braking pressure.

Further depression of the brake pedal 15 moves the wiper arm P over a second sector b of the rheostat 25 thereby increasing the voltage applied to the control box 10, which increases the energisation of the motor 11 and speed of the pump 16, to increase the flow of hydraulic fluid to the brake pistons 17 (N1 N2 in Figure 2.) Continued depression of the brake pedal 15 increases the motor energisation until a point is reached, in sector c of the rheostat at which the control box 10 drives the motor 11 at full speed (NP in Figure 2) and operates to shut off the electrically operable valve 22 so that all the hydraulic fluid being pumped from the reservoir is passed to the brake pistons 17.

If during the braking sequence the trailer begins to overrun the tractor a load sensing device 26 connected between the tractor and trailer feeds a signal to the control box 10 which in turn increases the energisation of the motor 11 to increase the braking force applied to the pistons 17 whereby to decrease the amount by which the trailer overruns the tractor.

The load sensing device 26 may be adjusted to give a simple on/off signal to the control box 10 -- for example causing the trailer brakes to be fully applied until the trailer is no longer overrunning the tractor. Alternatively the load sensing device may provide a signal directly proportional to the degree of trailer overrun and cause the trailer brakes to be applied to a degree dependent upon the amount by which the trailer is overrunning the tractor.

Should the tractor brakes fail or should the trailer become detached from the tractor, the system provides that a mechanical switch 27 is closed connecting the control box 10 to an auxiliary power supply 28 carried on the trailer which operates to drive the motor 11 at its top speed whilst holding shut the electrically operable valve 22.

In the alternative arrangement shown in Figure 3 only that part, A, of the system carried by the trailer is shown. Most of the parts shown in Figure 3 operate in the~manner described with reference to Figure 1 and corresponding parts carry the same reference numerals.

As can be seen in addition to the parts of the system described with reference to Figure 1 the arrangement of Figure 3 includes a pump 30 which is mechanically coupled to an axle of the trailer. The pump 30 is connected in the feed pipe from the reservoir 18 to the pump 16, which feed pipe also includes a normally closed electrically operable on-off valve 31.Valve 32 is connected to the control box 10 as shown.

As with the arrangement described with reference to Figure 1, when the wiper arm moves across the first sector of the rheostat the control box 10 drives motor 12 at chosen speed -- 25% of its maximum speed.

At the same time the control box 10 is arranged to open the normally closed electrically operated valve 31 so that pump 16 is supplied with hydraulic fluid from the reservoir 18 by the pump 30. The mechanical pump 30 is therefore used to provide a base pressure upon which the pump 16 acts.

As has already been described with reference to Figure 1 hydraulic fluid in the pipe 19 is diverted, at least in part via the normally .open valve 22 to the reservoir 18. The braking force applied to the brake pistons 17 of the trailer is therefore less than the maximum.

Further depression of the brake pedal moves the wiper arm over the second sector of the rheostat increasing the voltage supplied to the control box 10 which in turn increases the energisation of the motor 11 (and so the speed of the pump 16) to increase the flow of the hydraulic fluid to the brake piston. 17. Continued depression of brake pedal increases the motor energisation till that point is reached, in sector C of the rheostat, at which the control box 10 drives the motor 11 at full speed and operates to shut the electrically operable valve 22 so that all the hydraulic fluid being pumped from the reservoir via the pumps 30 and 16 passes to the brake pistons 17.

It will be appreciated that the above embodiments may be modified without departing from the scope of the invention, for example the systems may be used with air or vacuum braking systems, the speed of the motor being used to control energisation of a valve included in the system controlling the pressure applied to the brake pistons.

It will be appreciated that the advantages of the described embodiment are that the trailer is braked in proportion to, or in sequence with, the braking of the tractor, the braking of the trailer is independent from the braking of the tractor and that the trailer braking system operates to stop the trailer should the braking system of the tractor fail or should the trailer become separated from the tractor. And further that with the em bodiment of Figure 3 at least part of the braking effort is provided by the motion of the trailer itself.

WHAT WE CLAIM IS: 1. A braking system for a towed vehicle, comprising a fluid pressure generator operable to displace fluid from a reservoir into a distribution network having passage means communicating with one or more brake actuation chambers and a return branch to the reservoir, and control means for controlling operation of the fluid pressure generator to regulate the rate at which fluid is displaced thereby and thus control the braking force applied to the towed vehicle, said control means being responsive, when the towed vehicle is connected to a towing vehicle, to an electrical signal indicative of a desired rate of braking of said towing vehicle.

2. A system according to Claim 1, in which said control means causes a rate of fluid displacement- proportional to said electrical signal.

3. A system according to Claim 1 or Claim 2, including means responsive to movement of the towed vehicle to generate fluid pressure in the system.

4. A system according to any preceding claim, including means operable to measure, and to generate an electrical signal indicative of, the amount by which the towed vehicle overruns a towing vehicle to which it is con nected, and in which the control means is responsive to that electrical signal to in crease the braking force applied to the towed vehicle proportionally.

5. A system according to any preceding claim, including means operable to cause said fluid pressure generator to apply a maximum braking force to the towed vehicle if it becomes separated from a towing vehicle.

6. A system according to any preceding claim, in which said fluid pressure generator comprises an hydraulic pump driven by an electric motor the speed of which is controlled by the control means in dependence on said first-and/or said second-mentioned electrical signal.

7. A system according to any preceding claim, in which said return branch includes a normally open electrically operable valve arranged to be closed when a maximum braking force is to be applied to the towed vehicle.

8. A system according to claim 7, including a manually adjustable throttle valve in series with the electrically operable valve.

9. A system according to claim 3 and claim 6, in which said movement responsive means comprises a further pump interconnecting the reservoir and said hydraulic pump, said further pump operating to pump hydraulic fluid to said hydraulic pump at a rate which is proportional to the speed of the towed vehicle.

10. A system according to claim 9, in which said further pump is coupled mechanically to a moving part of the towed vehicle.

11. A system according to claim 10, in which said further pump is coupled to an axle of the towed vehicle.

12. A system according to claim 5, in which said means operable to cause said fluid pressure generator to apply a maximum braking force includes a normally closed switch arranged to be biased open when the towed and towing vehicles are coupled.

13. A system according to claim 6 or any claim dependent thereon, including an electrical battery for actuating the electric motor in the event of the towed vehicle being detached from a towing vehicle. 14. The combination of a towed vehicle, and a towing vehicle, in which the towed vehicle is provided with the braking system of any preceding claim, and the towing vehicle is provided with means for generating an electrical signal representative of a desired braking effort for said towing vehicle.

15. The combination of claim 14, in which said means for generating an electrical signal comorises a variable resistance element coupled to a driver's brake pedal of the towing vehicle.

16. A braking system substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.

17. A braking system substantially as herein described with reference to Figure 1 as modified by Figure 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. bodiment of Figure 3 at least part of the braking effort is provided by the motion of the trailer itself. WHAT WE CLAIM IS:

1. A braking system for a towed vehicle, comprising a fluid pressure generator operable to displace fluid from a reservoir into a distribution network having passage means communicating with one or more brake actuation chambers and a return branch to the reservoir, and control means for controlling operation of the fluid pressure generator to regulate the rate at which fluid is displaced thereby and thus control the braking force applied to the towed vehicle, said control means being responsive, when the towed vehicle is connected to a towing vehicle, to an electrical signal indicative of a desired rate of braking of said towing vehicle.

13. A system according to claim 6 or any claim dependent thereon, including an electrical battery for actuating the electric motor in the event of the towed vehicle being detached from a towing vehicle.

14. The combination of a towed vehicle, and a towing vehicle, in which the towed vehicle is provided with the braking system of any preceding claim, and the towing vehicle is provided with means for generating an electrical signal representative of a desired braking effort for said towing vehicle.