ESTA makes gear changes easy byMartin Hayes
Page 30
Page 31
If you've noticed an error in this article please click here to report it so we can fix it.
New Ford semi-automatic uses mini-computer
IN WHAT could be one of the most significant technical developments of 1974 Ford yesterday released I details of a new semi-automatic transmission system suitable for use with its 468 gearbox range. The new gearbox is known as ESTA — Electronically Synchronized Transmission Assembly. First developments of the system are aimed at the psv market but there is clear potential for onand off-road truck appli cations, too.
A 45-seat Alexanderbodied Ford R1014 fitted with the new ESTA sixspeed transmission enters trial service with Maidstone Corporation next week and five further vehicles should be in operational service by September. Two of these will probably be trucks. A vehicle with a fully automatic version of the transmission should be operating by the end of the year. ESTA is designed for use with the four-, sixand eight-speed transmissions in the 468 range without major modifications as original equipment.
Essentially the semi-automatic version uses a mini digital computer to control --by means of hydraulic ser vos the operation of clutch, throttle and gear selector mechanism. Because engine and layshaft synchronization is able to be accurately controlled — down to a tolerance of 30 rpm — the synchromesh cones are omitted from what is otherwise a standard gearbox and clutch unit.
The essence of the transmission is its electronic con trol unit which utilizes advanced electronic techniques. Ford engineers initially compiled a basic logic programme but the production control unit or black box has been de veloped with extensive assistance from Ferranti.
One of the major problems with semi-automatic gearboxes of this type in the past has been precise control of clutch action. The ESTA system embodied a very sensitive clutch control system. In effect, clutch slip moving off from rest is governed by the accelerator position. As the throttle is depressed so the amount of slip is reduced until the clutch locks up completely and becomes fully engaged.
Engagement takes place at a controlled rate during all gearchanges on the move. The control unit also allows the clutch to disengage at low road or engine speed.
The electronic control unit — the size of which will be substantially reduced in mass production by the use of miniaturized "chips" — receives signals from two sources: the accelerator and the gear selector switch. It also monitors engine speed by means of a transducer on the starter ring gear and road speed by a gear mounted on the universal coupling behind the gearbox.
When a gear is selected the unit uses the road speed to compute the necessary engine speed for perfect synchronization and adjusts the engine speed accordingly. 'his latter process is ccomplished by the throttle the case of a speed icrease and by an exhaust Take in case of a decrease. )nce the speeds are synhronized the gear selection made. If for any reason the ear change is baulked the .ontrol unit will recycle until he selected gear is obtained.
The ESTA system uses lectronics to control the tear change exercise and iydraulics and pneumatics o operate actuators to carry t out. The black box decries consume less power :han the direction indicator Ind can be easily removed ind dispatched for expert maintenance. The hydraulic system which operates the actuators — mounted on top of the standard gearbox casing is the only item which is expected to require regular maintenance and this only in keeping a check on the oil level.
Because the synchromesh cones are removed — making the unit a crash box in fact — there is, it is claimed, a marginal weight saving. Ford engineers expect that the life of driveline components should be increased because the possi bility of driver abuse is eliminated. Should too low a gear be selected at too high a road speed the engine is automatically boosted to maxi mum governed speed but the gear will not engage until the road speed falls to the correct level. Similarly, if too high a gear is engaged on the move the system guards against stalling.
On the road Ford allowed journalists to drive the bus fitted with ESTA around the small test track at the company's Dunton research and engineering centre. Though there was inadequate time or distance to assess the system fully it was clear that it has tremendous potential.
The gear selector has eight positions — reverse, a separate neutral slot and six forward gear positions in a conventional gate. There is no obstruction to any gear being engaged which means that gears can be omitted if desired. The engine can be started only in the neutral position.
The selector itself looked and felt very like that used by Self Changing Gears in its pneumocyclic box, which made driving initially a little confusing. The ESTA unit does not have a neutral position between the gears — the lever can be moved around the gate without the previous gear being disengaged until the next is positively selected.
On moving off there is a quite surprising amount of "feel" of the clutch take-up through the throttle — it literally is a two-in-one pedal. The faster one presses the pedal down the more sharply the clutch comes in — and vice versa. Once on the move upwards changes are considerably smoothed if one eases back on the pedal. Because the actual change happens very fast indeed it takes a little while to accustom oneself to the proper , timing here.
On down changes, however, things are much easier — not to say uncanny. Select fifth from sixth, for example, at 72 km/ h (45 mph) and the accelerator slaps on to the floor all by itself, just as an experienced driver would treat it during a double-declutch exercise. The gear engages smoothly and the driver gets a round of applause from his passengers — without ever having done a thing except move the selector lever!
In the interests of true evaluation I tried hard to abuse the transmission. 1 engaged 1st gear at 80 km1 h (50 mph). Just as the engineers said, the engine went straight up to its governed maximum and we cruised along in "neutral" until the road-speed fell to the correct level and the gear engaged. I did manage to stall the bus — but only by stamping down on the throttle with 4th gear engaged at rest. Using some care I was then able to restart and by slipping the clutch sufficiently, get the vehicle away in this gear.
Though Ford is reluctant to put a price on its new transmission it seems likely that it will add about £500 to the chassis price. This is about half the extra currently required for a Ford psv chassis fitted with the SCO box. An automatic version would be relatively little more expensive. Both prices could fall if yolume produc tion were achieved, when the cost of the electrics would be less.
At first sight the ESTA system seems to be a wel come development. With the exception of the electrical components it utilizes a really simplified gearbox and few additional components which are likely to give trouble. It avoids the difficulties and thirst for fuel of torque converter transmissions by relying on the conventional clutch. This in fact may be its weakness too. The only possible abuse seems to be in holding the vehicles ori hills by slipping the clutch. Only operational service will tell if this is a true weakness. I hope to report shortly on a longer spell at the wheel to see just what ESTA does when confronted by traffic and hills.
Major bus operators have already expressed considerable interest in ESTA and several will shortly be helping with its evaluation. I would imagine that many of them may well find a fully automatic version even more attractive because, with multi-speed gearboxes at least, driving ESTA may prove a little complicated initially.