GB1601575A

GB1601575A - Combined dynamic and friction vehicle braking system

Info

Publication number: GB1601575A
Application number: GB22920/77A
Authority: GB
Original assignee: Westinghouse Brake and Signal Co Ltd
Current assignee: Siemens Mobility Ltd
Priority date: 1977-05-31
Filing date: 1977-05-31
Publication date: 1981-10-28
Also published as: AU521972B2; AU3653278A; NZ187372A; ZA782889B

Description

(54) A COMBINED DYNAMIC AND FRICTION VEHICLE BRAKING SYSTEM (71) We, WESTINGHOUSE BRAKE AND SIGNAL COMPANY LIMITED, a Company incorporated under the Laws of Great Britian, of 3, John Street, London, WCIN 2ES, England, do hereby declare 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 vehicle braking systems and vehicles incorporating such brakings systems.

There are two common methods of braking vehicles, one of which is by the application of friction brakes, and the other by dynamic e.g. regenerative braking.

Available dynamic braking effort diminishes with diminishing vehicle speed, and is usually of little useful effect below a speed dependent on the form of dynamic braking employed. Therefore as vehicle speed diminishes, it eventually becomes no longer possible to rely on dynamic braking, and friction brakes must then be employed, which are effective at all speed down to complete vehicle standstill.

In the case of a vehicle, which may be a road vehicle or a railway vehicle, comprising a first part providing traction power and one or more further parts which are unpowered and are propelled and/or towed by the first part, it has been proposed that upon a braking effort being demanded by the vehicle's driver, braking shall be provided on the different parts of the vehicles according to their respective weights; in the case of the first powered part, by dynamic braking as far as possible and then by friction braking; and in the case of the other unpowered parts by friction braking; in all cases the braking effort on each part being according to the demanded braking level. For demanded braking levels less than full level, the dynamic brake is incompletely employed, and despite there being a reserve of dynamic braking power available, friction braking is employed.

It is therefore an object of the invention to provide a vehicle braking system which more usefully employs available dynamic braking.

According to one feature of the invention a vehicle braking system comprises dynamic braking means, friction braking means, braking demand signal generating means adapted for operation by a driver to select a braking level and brake application control means responsive to the braking demand signal generating means to automatically actuate the braking means sequentially wherein for a selected braking level in a first range up to a maximum obtainable dynamic braking effort the dynamic braking means only is brought into operation and for a selected braking level in a second range the friction braking means is automatically brought into operation to augment the total braking effort.

In one embodiment of the invention, three wires are used to control seven steps of dynamic braking, and a further three wires are used to control a further seven steps of friction braking (making fourteen steps of braking with dynamic braking being initially applied substantially without any friction braking).

Thereby the dynamic braking capability is employed as much as possible substantially without the friction braking, until it is necessary to supplement the diminishing maximum available dynamic braking effort with friction braking, the friction braking thereby being kept to the minimum.

In an alternative arrangement of conductors, four conductors are employed, three for controlling seven steps of dynamic braking effort, and then when the fourth conductor is energised or de-energised, the signals on the first three conductors controlling seven additional steps of friction braking effort while maintaining maximum available dynamic braking effort.

In order that the invention may be more clearly understood and readily carried into effect, preferred embodiments of the same will now be described with reference to the accompanying drawings wherein: Fig. I is a schematic diagram of a first embodiment of the invention: and Fig. 2 is an electrical schematic diagram of a second embodiment of the invention.

Referring first to Fig. I, this diagrammatically illustrates a "7 plus 7" Westcode (Registered Trade Mark) system in accordance with the invention. This system is applied to a driving power coach 10 and a trailer coach 12. In the power coach 10 are the conventional traction controls (not shown) and brake application control means consisting of a modified Westcode brake controller 14. The controller 14 is such as to deliver, upon operation of a braking demand signal generating means, that is, rotation of a brake controlling handle 16 from a "brakes fully released" position, Gray-coded electrical signals along a first set of three trains wires Al, Bl and Cl.These signals command dynamic braking, as about to be described, in seven steps up to maximum available dynamic braking, for a first part of the range of movement of the handle 16. (The effect of movement of the handle 16 in a further, second range of movement will be described later).

The Gray-coded signals on the wires Al, B I and C1 are tapped off by a signalresponsive code converter 18 which converts the commanded braking level (set by the degree or rotation of the handle 16 in its first range of movement) to an appropriate level of traction motor excitation schematically denoted by a motor field coil 20 which interacts in known manner with the traction motor armature 22 to generate electric power which is dissipated in a resistor 24 connected across.the armature 22, thereby to effect dynamic braking in known manner. The armature 22 is shown connected to a powered coach wheel 26 by a mechanical linkage 28 which may be a direct armature-to-axle connection, or be by way of one or two stages of mechanical gear speed reduction.The wheel 26 is, of course, one of a pair secured to an axle (not shown) of the coach 10, and the coach 10 will normally have two such two-wheeled axles, one or both of which may be motored and hence dynamically brakable, or two multi-axle bogies, one or all of the axles on each bogie being motored and hence dynamically brakable. (Only one wheel and one motor are shown in Fig. I for the sake of simplicity). The resistor 24 is shown as a single fixed-value resistor for the sake of simplicity, but could be a stepped resistor or a plurality of resistors whose net resistance is controlled by suitable electric switches (not shown) under the control of the converter 18. Omitted for clarity is the switch by which the resistor 24 is disconnected from the armature 22 when the armature 22 is no longer required for dynamic braking, e.g. when the armature 22 is required to deliver tractive power.

Braking of the wheel 26 may be by dynamic braking only, in which case the pneumatically actuated friction braking equipment about to be described may be omitted, but it is preferred that braking of the wheel 26 and associated wheels (not shown) on the coach 10 be supplemented as required by pneumatic friction braking now to be described. For the purpose of friction braking of the wheel 26, a friction brake shoe 30 of known form is pivoted at a point 32 for controlled and anchored contact with the tread of the wheel 26, the friction produced by contact between the wheel 26 and the brake shoe 30 varying according to the applied pressure therebetween and producing corresponding variations of the friction braking effort on the wheel 26, as is well known in the art of railways.Movement of the brake shoe 30 and its pressure against the wheel 26 is effected by a pneumatic piston 34 slideable within a cylinder 36, the piston 34 and the cylinder 36 together constituting a known form of fluid-pressure motor. Pneumatic pressure is applied to the cylinder 36. thereby to produce a thrust on the piston 34, from a pressure source shown schematically as an auxiliarv air-pressure reservoir 38. the pressure actually applied to and exhausted from the cylinder 36 being under the control of a pneumatic control valve 40 which may be any suitable known form of electropneumatic control valve or a triple valve. The valve 40 is under the control of the converter 18 to supplement the dynamic braking effort as it falls off ith diminishing vehicle speed or other limiting effect to keep the net braking effort substantially at the effort demanded bv the controller 14. The reservoir 38 is charged xxith compressed air from an air compressor (not shown) delivering air along a train pipe (not shown), the train pipe also delivering air to a similar reservoir on the coach 12 if that reservoir (subsequently to be described) is not supplied by a further compressor (not shown) on the coach 12.

It is preferred that the converter 18 causes friction braking of substantially equal effort to the preceding dynamic braking effort in the event of failure of the dynamic brake, without calling on the friction braking on the coach 12 to make up the dynamic braking deficiency.

Movement of the brake controlling handle 16 in its first range of movement commands seven different levels of dynamic braking effort, supplemented as required by friction braking if provided on the coach 10, up to a maximum braking effort which in the limiting case is determined by the available adhesion of the wheel 26 and like-braked wheels (not shown) on the coach 10 or is determined by a limiting stress on the intercoach coupling (not shown).

Assuming now that a higher braking effort is demanded by the movement of the handle 16 into a second further range of its movement away from the brakesreleased position towards maximum braking effort, this higher braking effort being above what can be obtained from braking effort on the coach 10, friction brakes on the coach 12 are brought into operation by maintaining the signals on the train wires Al, Bl and Cl in the combination thereof demanding maximum braking effort from the coach 10, and at the same time applying Gray-coded signals on a further three main train wires A2, B2 and C2 extending from the controller 14 to the coach 12, the signals on the wires A2, B2 and C2 being according to which one of seven further braking levels is demanded.

For the sake of simplicity, only one wheel 42 is shown on the coach 12, but there would in practice be two two-wheeled axles, or two two-axle or three-axle bogies (each with four or six wheels), each being friction-brakable as will now be described with reference to the wheel 42. The friction braking mechanism on the coach 12 can be identical to the friction braking mechanism on the coach 10, and thus comprises a brake shoe 44 pivotally anchored at a point 46, a shoe-applying piston 48 acted upon by air pressure in a cylinder 50, the air pressure coming from an air-pressure reservoir 52 under the control of a valve 54 actuated by control signals from a signal converter 56 coupled to the wires A2, B2 and C2 to be suitably responsive to the Gray-coded signals thereon.

The seven steps of dynamic braking effort on the coach 10 can thus be augmented by a further seven steps of friction braking effort on the coach 12, dynamic braking on the coach 10 (supplemented if desired by friction braking solely on the coach 10) taking precedence up to the limit of braking effort available on the coach 10 before friction braking effort on the coach 12 is commanded into effect. Thereby full use is made of dynamic braking before friction braking of the non-dynamically braked wheels is effected.

All six wires Al, BI, Cl, A2. B2, and C2; are run through each coach 10 and 12, connections between the coaches 10 and 12 being by a six-pole jumper 58 incorporating a seventh current path (not shown) for return current, the return current path not necessarily being a discrete conductor but possibly simply the metallic chassis and bodywork of the coaches with inter-coach connection being by means of mutually contacting metallic housings of the two parts of the jumper 58.

The jumper 58 may incorporate a train pipe connection (not shown) for conveying compressed air down the length of the train.

A further jumper 60 is provided so that the two-coach train brake control may be extended to added further coaches such as may be by way of coupling together two or more two-coach trains to form four, six. or more coach trains, as is known in the operation of railwavs. Thus extensions of-the Al, B1 and Cl wires enable control of dynamic braking on any further power coaches that may be added. and the extensions of the A2, B2 and C2 wires enable the control of friction braking on any further non-dynamically friction braked coaches.

As applied to a locomotive or multiple-unit having a driving position at either end of the locomotive or unit, there would be one of the brake controllers 14 at each of the driving positions together with interlocks, such as key-operated switches of known form. to prevent more than one brake controller being effective at anv one time. Only one driving position and one brake controller is shown in Fig.

I for the sake of simplicity.

The arrangement of Fig. 1 may be considered as two specially applied Westcode controllers integrated into a single controller and cascaded for mutually sequential operation. This accounts for the duplication of the conventional Westcode "A", '.13" and "C" wires.

Fig. ' illustrates a modification of the arrangement of Fig. 1. the arrangement of Fig. 2 being based on the principle that only four binary or Gray coded wires are necessary to transmit fourteen steps of braking command signals. Relay switching arrangements are utilised to decode braking command signals into the requisite dynamic and then friction braking control signals.

Dealing now in detail with Fig. 2, there are, as in Fig. 1, a power coach 10, and a trailer (non-powered) coach 12. The power coach 10 includes a brake controller 15 corresponding in function (but not in detail) to the controller 14 of Fig. 1.

Extending down the train, between and along the coaches 10 and 12 (and any other coaches (not shown)) are six train wires, namely an EPA wire, an EPB wire, an EPC wire, and an EPD wire and +ve and -ve supply lines energised by any suitable source (not shown) such as a battery, or a solid-state chopper or motor-dynamo set powered by the traction supply. Switches 62. 64, 66, 68, 70 and 72 within the controller 15 are shown their open-circuit positions, and are opened and closed by a suitable shaped cam or cams (not shown) turned about an axis by operation of the single brake controlling handle (not shown in Fig. 2).The effect of opening and closing the switches 62-72 is to cause suitable Gray-coded energisations ana deenergisations of the wires EPA, EPB, EPC, and EPD which are converted in a relay unit 74 in the coach 10 to dynamic brake controlling signals and in a relay unit 76 in the coach 12 to friction braking signals, the braking signals in each case appearing as binary-weighted digital signals on respective A, B, and C wires (with a -ve return) corresponding to the A, B, and C wires of a conventional Westcode brake control unit.

The preferred energisation and de-energisation of the wires EPA, EPB, EPC, and EPD is such as to provide an "energise to release" braking control system whereby any fault such as loss of signal power supply, breaking or earthing of any train wire, or relay closure failure will result in at least partial application of the train brakes, the system thereby being "fail-safe".

Within the relay unit 74, a single relay coil 78 operates twin-ganged normally open contacts 80, a twin-coil relay 82 polarised as shown operates twin-ganged normally open contacts 84, a twin-coil relay 86 polarised as shown operates twinganged normally open contacts 88, and a twin-coil relay 90 polarised as shown operates a single pole normally open contact 92.

Within the relay unit 76, a single coil relay 94 operates triple-ganged normally open contacts 96, a single coil relay 98 operates twin-ganged normally open contacts 100, a twin-coil relay 102 polarised as shown operates twin-ganged normally open contacts 104, and a twin-coil relay 106 polarised as shown operates a single pole normally open contact 108.

A relay coil 110, when de-energised, operates means not shown in Fig. 2 for inhibiting dynamic braking in "release" and "emergency" braking situations, as may be seen from the following table.

There now follows a table setting out successive operations of the switches 62-72 to effect braking of the train from full brake release through thirteen steps of service braking and a fourteenth step of emergency braking. It is to be assumed that the braking signal responsive unit on the coach 10 in Fig. 2 which responds to the signals on the respective wires A, B and C, functions as does the unit 18 in Fig.

1, to control dynamic braking and possible supplemental friction braking, and that the corresponding unit (not shown in Fig. 2) which responds to the signals on the respective wires A, B, and C in the coach 12 functions as does the unit 56 in Fig. 1.

It is further to be assumed that the coach 10 in Fig. 2 has the same dynamic braking and friction braking equipment (not shown in Fig. 2) as shown in the coach 10 in Fig.

1, and that the coach 12 in Fig. 2 has the same friction braking equipment (not shown in Fig. 2) as shown in the coach 12 in Fig. 1.

In the following table, a "1" indicates that a conductor is energised or that a contact is closed, as the case may be, and a "0" indicates that a conductor is deenergised or that a contact is open, as the case may be.

Commanded Controller Switches Wires on Wires on braking Coach 10 Coach 12 level .62 64 66 68 70 72 . A B C . A B C release 0 0 0 1 1 0 1 1 1 1 1 1001 1 1 1 l l l l 2 1 1 0 1 0 1 1 0 1 1 1 1 3 0 1 0 1 0 1 0 0 1 1 1 1 4 0 1 1 1 0 1 1 1 0 1 1 1 5 1 1 1 1 O 1 0 1 1 1 6 1 0 1 1 0 1 100 111 7 1 0 1 0 0 1 0 0 0 0 1 1 8 1 11001 0 0 0 101 9 0 I 1001 l 0 0 1 10 0 1 0 0 0 1 0 0 0 1 1 0 11 1 1 0 0 0 1 0 0 0 0 1 0 12 1 0 0 0 0 1 0 0 0 1 0 0 13 0 0 0 0 0 1 0 0 0 0 0 0 (full service) emergency 0 0 0 0 0 0 0 0 0 0 0 0 It is to be noted from the table that simultaneously with a command for maximum dynamic braking on the coach 10 (step 7), it is preferred to initiate the first step of friction braking on the coach 12. This is to avoid the situation that would otherwise arise when using a Gray-code signalling system (i.e. only one controller switch may be operated at a time), in which there would be a step after full dynamic braking had been commanded before friction braking would be called for, i.e. the train controller would have to make two brake controller steps to make one braking effort step.

"Emergency" braking is the full application of air braking on both coaches 10 and 12 with dynamic braking inhibited.

It will be noted that the relay units 74 and 76 convert the Gray-coded signals from switches 62-70 to binary coded signals on the wires A, B and C on each of the coaches 10 and 12 in succession.

In the normal circumstances of a train having a brake controller 15 at either end thereof, suitable switch means, such as a driver's key-operated drum switch of known form will be incorporated in the brake controllers or in the train wires leading therefrom for rendering ineffective the controller or controllers not in use, and preferably being such as to earth or ground or short-circuit the inoperative controller's outputs to prevent inadvertant and undesirable stray signals. Not shown in Fig. 2 are optional switches or other means operable by a guard or a passenger to initiate emergency braking regardless of the commanded braking effort at the time when emergency braking is commanded.

WHAT WE CLAIM IS: 1. A vehicle braking system comprising dynamic braking means, friction braking means, braking demand signal generating means adapted for operation by a driver to select a braking level and brake application control means responsive to the braking demand signal generating means to automatically actuate the braking means sequentially wherein for a selected braking level in a first range up to the maximum obtainable dynamic braking effort the dynamic braking means only is brought into operation and for a selected braking level in a second range the friction braking means is automatically brought into operation to augment the total braking effort.

2. A vehicle braking system according to Claim 1, wherein the dynamic braking means acts only with respect to driven axles and the friction braking means acts only with respect to undriven axles.

3. A vehicle braking system according to Claim 1 or Claim 2 including a pluralitv of braking of braking demand signal generating means for a vehicle having a plurality of driving positions wherein each has a respective braking demand signal generating means.

4. A vehicle braking system according to Claim 3, wherein each braking demand signal generating means is connected to a common brake application control means through a respective switch.

5. A vehicle braking system according to Claim 3, wherein each braking demand signal generating means is connected to a respective brake application

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

Claims

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

Commanded Controller Switches Wires on Wires on braking Coach 10 Coach 12 level .62 64 66 68 70 72 . A B C . A B C release 0 0 0 1 1 0 1 1 1 1 1 1001 1 1 1 l l l l

2 1 1 0 1 0 1 1 0 1 1 1 1

3 0 1 0 1 0 1 0 0 1 1 1 1

4 0 1 1 1 0 1 1 1 0 1 1 1 5 1 1 1 1 O 1 0 1 1 1

6 1 0 1 1 0 1 100 111

7 1 0 1 0 0 1 0 0 0 0 1 1

8 1 11001 0 0 0 101

9 0 I 1001 l 0 0 1

10 0 1 0 0 0 1 0 0 0 1 1 0

11 1 1 0 0 0 1 0 0 0 0 1 0

12 1 0 0 0 0 1 0 0 0 1 0 0

13 0 0 0 0 0 1 0 0 0 0 0 0 (full service) emergency 0 0 0 0 0 0 0 0 0 0 0 0 It is to be noted from the table that simultaneously with a command for maximum dynamic braking on the coach 10 (step 7), it is preferred to initiate the first step of friction braking on the coach 12. This is to avoid the situation that would otherwise arise when using a Gray-code signalling system (i.e. only one controller switch may be operated at a time), in which there would be a step after full dynamic braking had been commanded before friction braking would be called for, i.e. the train controller would have to make two brake controller steps to make one braking effort step.

"Emergency" braking is the full application of air braking on both coaches 10 and 12 with dynamic braking inhibited.

It will be noted that the relay units 74 and 76 convert the Gray-coded signals from switches 62-70 to binary coded signals on the wires A, B and C on each of the coaches 10 and 12 in succession.

In the normal circumstances of a train having a brake controller 15 at either end thereof, suitable switch means, such as a driver's key-operated drum switch of known form will be incorporated in the brake controllers or in the train wires leading therefrom for rendering ineffective the controller or controllers not in use, and preferably being such as to earth or ground or short-circuit the inoperative controller's outputs to prevent inadvertant and undesirable stray signals. Not shown in Fig. 2 are optional switches or other means operable by a guard or a passenger to initiate emergency braking regardless of the commanded braking effort at the time when emergency braking is commanded.

WHAT WE CLAIM IS: 1. A vehicle braking system comprising dynamic braking means, friction braking means, braking demand signal generating means adapted for operation by a driver to select a braking level and brake application control means responsive to the braking demand signal generating means to automatically actuate the braking means sequentially wherein for a selected braking level in a first range up to the maximum obtainable dynamic braking effort the dynamic braking means only is brought into operation and for a selected braking level in a second range the friction braking means is automatically brought into operation to augment the total braking effort.
2. A vehicle braking system according to Claim 1, wherein the dynamic braking means acts only with respect to driven axles and the friction braking means acts only with respect to undriven axles.
3. A vehicle braking system according to Claim 1 or Claim 2 including a pluralitv of braking of braking demand signal generating means for a vehicle having a plurality of driving positions wherein each has a respective braking demand signal generating means.
4. A vehicle braking system according to Claim 3, wherein each braking demand signal generating means is connected to a common brake application control means through a respective switch.
5. A vehicle braking system according to Claim 3, wherein each braking demand signal generating means is connected to a respective brake application

control means and a switch is provided for selectively connecting the brake application control means to the braking means.
6. A vehicle braking system according to any preceding claim, wherein the brake application control means is operative to generate electrical signals adapted to actuate the braking means.
7. A vehicle braking system according to Claim 6, wherein the electrical signals generated by the brake application control means comprise coded binary digital signals.
8. A vehicle braking system according to Claim 7, wherein the coded signals comprise two groups each of three binary digits so that each group provides for seven brake application steps and the dynamic braking means is responsive to one group and the friction braking means is responsive to the other group to provide up to a total of fourteen brake application steps.
9. A vehicle braking system according to Claim 7, wherein the coded signals comprise one group of three binary digits, providing for seven brake application steps. and a fourth binary digit arranged to actuate in one state the dynamic braking means only and in its alternative state to actuate the dynamic braking means and the friction braking means.
10. A vehicle braking system according to any one of Claims 7, 8 or 9, wherein the digital code comprises binary Gray code.
11. A vehicle incorporating a braking system according to any preceding claim.
12. A vehicle according to Claim 11, being a railway vehicle.
13. A railway vehicle according to Claim 12 comprising at least one powered coach and at least one unpowered coach wherein the dynamic braking means is fitted to the powered coach and the friction braking means is fitted to the unpowered coach.
14. A braking system substantially as described, with reference to Fig. I or Fig.

2 of the accompanying drawings.
15. A railway vehicle or train fitted with a braking system substantially as described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.