Brakes Have an Easy. Time with the New Kim
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!derBy R. D. CATER DIGGER demands on braking systems, 1-1 being made daily by worsening traffic conditions, higher road speeds, the extension of the motorway networks and not least by the increases in size and payload of vehicles, are creating almost insurmountable problems for the transport engineer. Continual replacement of linings, often at ridiculously low mileages, accompanied by the frequent renewal of brake drums and the loss of operating time are contributing in no small way to the soaring cost of vehicle maintenance. To this must be added the decreasing 'efficiency of conventional braking systems when subjected to repeated heavy, application, through the build-up of heat and the inevitable fade that accompanies it.
For some years I have been convinced that the drum brake as we know it must be nearing the end of its useful application as a service brake on commercial vehicles. This type of brake is still doing an extremely good job, but the rising cost of operating the drum/shoe unit is fast becoming prohibitive. In my opinion, the direction in which everything points is that of the non-wearing transmission fietarder.
A few months back I experimented with a Tapley meter to discover the maximum retardation that I used on my daily trip to the office. Excluding emergencies, it proved to be around 12 per cent; on some of the occasions when somebody did something stupid, this tigure climbed to 18 to 20 per cent. In the three days that I kept the Tapley in use—and this represented 240 miles on one of the most heavily trafficked commuter roads around London—the Tapley never went above 25 per cent. I noted these figures for future reference.
My first opportunity to test the usefulness of a retarder came recently when I did a trip from Cardiff to Glasgow with a vehicle so fitted (The Commercial Motor, August 6). Only two applications of the normal wheel brakes were made CS throughout the whole journey. The second opportunity came last week when a new electric retarder, which is being imported into the country and marketed by a company formed expressly for the purpose, was offered for appraisal. Called the Klam Superbrake retarder, the unit is marketed by Eesubrake of 9 Nottingham Road, Isleworth, Middx. (tel. Isleworth 7144).
Stator and Rotor It consists of two fundamental parts: the stator, which is fixed to the chassis in the position normally occupied by the centre propeller-shaft bearing, and carries a number of copper-cored coils and a pair of substantial taper-roller bearings; and the rotor, which comprises a shaft carrying two discs in which Foucault currents are developed, so producing resistance to the rotation of the shaft. A remote control lever (energizing through solenoids the control box, which in turn energizes a predetermined number of coils) is mounted on the steering column or in some other convenient position and has five notches; " off ", and I to 4.
When the first position is selected the contactor box energizes four coils and at 30 m.p.h. this produces 5 per cent retardation on the Tapley meter. Selecting position number two energizes eight coils and this produces 8 per cent on the Tapley at 30 m.p.h. The third position energizes 12 coils giving 121 per cent and the fourth position energizes the whole assembly of 16 coils, producing 15 per cent on the Tapley meter.
Six different sizes of retarder are available, ranging from the one tested, which was suitable for operation with gross vehicle weights of up to 10 tons, up to the largest capable of application to heavy haulage vehicles, dumpers and the like. Energy for the coils is produced front the vehicle batteries and although the current drain is fairly high it is claimed that experience has shown that only when a luxury coach utilizing all its
lights, both heaters and screenwipers, has needed to use the retarder on number. four position while descending an Alpine pass, and then stopped at the bottom, was the drain from the battery enough to prevent the engine being restarted on the starter. This experience has prevented the same thing happening a second time, and the inclusion of alternators on the later passenger vehicles has eliminated it almost completely.
was told of a vehicle used on Continental touring, which had completed 100,000 miles and not needed brakes relining, when similar machines on the same job were being given brake overhauls at only 15,000 miles, and invariably required drums replacing. A point which must not be overlooked is the safety factor in having all the brake drums cold, or almost cold, at the end of a long descent or the end of a trip through dense traffic.
The test vehicle was a Bedford VAL 52-seater luxury coach, with bodywork by Platoon, belonging to Silverline Tours of Hounslow, Middx. Loaded with 10 people and ballast simulating a further 42 passengers the vehicle scaled 0 tons 13:5 cwt. My impressions of the retarder were gained in driving the vehicle from London Airport to a point east of Liphook, Hampshire. At this point, descending a test hill 0.3 miles tong, with an average gradient of I in 7 and a maximum gradient of 1 in 5, the retarder operating in fourth position (with the vehicle in top gear) held the road speed down to 18 m.p.h. with no assistance from the footbrake.
General handling on the road proved to be excellent and the only times that the footbrake was needed were when making the final effort to stop in traffic_ Below 5 m.p.h. the retarder has little or no effect. Apart from these moments I used the retarder at all times and soon became used to not applying the footbrake to check progress. Riding as a passenger in the coach I felt that the smooth ride, with absolutely no effort being made by the driver to accomplish this, must inevitably prove attractive.
The test vehicle was only a month old, but operating as it does on six tours a week—three from London to Stratford on and three from London to )rd. Winchester. Salisbury and mge -it already had 11.694 miles clock at the time of the test. And lot, according to its owner, at that teded a brake adjustment. This the fact that the average speeds ; tours are 35.25 m.p.h. and 31 respectively.
are, of course. penalties which the retarder, the first being the The unit fitted to the test vehicle 374 lb. whilst the biggest unit le weighs 496 113. To these weights c added approximately 56 lb. for ckets and mountings. Price must. se, be offset against future savings ation. The test unit cost t:220 10s. 8 10s. to fit, whilst the biggest unit plus £50 for fitting. Average time o instal the unit is SI hours and !. apart from the two taper roller s. there are no wearing parts the ri be transferred to a new vehicle le old one is replaced.
definition of a towing implement w includes a case where the drawn is partially suspended from the en. This was made effective with ling into operation on August 31 Motor Vehicles (Construction and limendment) (No. 2) Regulations 10. 1625. (HMSO. price 3c1.) amendment also modifies Section