Automatic Gearboxes PDF - Emergency Ambulance Response Driver's Handbook

6 Automatic Gearboxes Learning outcomes By the end of this chapter you should: i Understand the functionality of the selector lever options. Know the principles of how and when to manually select lock do^, sport onmanual modes within the gearbox special...

6 Automatic Gearboxes Learning outcomes By the end of this chapter you should: i Understand the functionality of the selector lever options. Know the principles of how and when to manually select lock do^, sport onmanual modes within the gearbox special prdframmes. Recognise the iiT|portant characteristics of automatic gearboxes. Understand the terms 'creep', 'run on' and 'lock down'. Understand how to get the most out of an automatic transmission when driving an emergency response vehicle. (T r  Emergency Ambulance Response Driver’s Handbook - these Many ambulance vehicles are fitted with an automatic transmission systems replace the need for a conventional clutch and gearbox so that the driver no longer has to shift gears manually. It is important that adequate training is received in their use in order for you to drive the vehicles correctly and safely, As automatic gearboxes are becoming more common, it is essential that you know how to make the best use of them. This chapter outlines the general principles of automatic gearboxes - understanding them will enable you to make correct decisions, based on accurate driving plans with due consideration to the presence of various hazards and the performance of the vehicle. / I Selector lever options / ( The selector lever is normally mounted on the dashboard, but it is sometimes on the floor or steering column, an example of which can be seen in Figure 6,1. Some vehicles have paddles or push-button mechanisms, so you should ensure through your PDC, and by reading the vehicle handbook, that you are familiar with the vehicle's selector lever and automatic gearbox controls. An illuminated indicator panel, usually contained within LCD display on the dashboard, provides visual confirmation of the selector position currently engaged. There are variations to the location of controls in automatic vehicles, but the function and principles remain the same. The basic selector lever positions are explained below. P (park) I 'Park' should be selected when the vehicle is parked, before the engine is 1 switched off, A check should be made that the selector is in this position before A attempting to start the engine. To further ensure safety, the footbrake should be depressed while starting the engine. Never move the lever to the 'P' position while the vehicle is in motion. R (reverse) 'Reverse' is usually located next to 'Park' in the selector mechanism sequence. It is normally a requirement of the system that the footbrake is depressed when moving the selector from 'P' to 'R’, or when moving from 'P' through 'R' to get to 62  Automatic Gearboxes another selector option. The vehicle may begin to move backwards the instant the selector is moved into 'R', unless the brakes are applied. N (neutral) No power is transmitted from the engine to the drive wheels when in neutral. It should be selected when the vehicle needs to be towed after a breakdown or accident. It should not be selected when , ,, temporary stops in traffic. You should consult the vehicle manual before towing or allowing the vehicle to be towed, as some systems may be damaged when the lever is left in 'N’and the vehicle’s wheels are moving. D (drive) 'Drive' is the regular operational mode to use when driving an automatic vehicle under normal driving conditions. It allows the transmission to make automatic adjustments according to your speed, engine loading and accelerator position. As the accelerator Is depressed, and the vehicle gathers speed, sensors detect the optimum time to change up to the next highest gear. The change is made automatically, without the intervention of the driver. Harsh acceleration can result in jerky changes, while smooth and gradual increases in speed may make changes imperceptible to patients and other passengers. Driving styles Many modern automatic gearboxes adjust to the driver's driving style, holding a gear for longer and delaying an upshift when accelerating quickly, while changing up earlier when applying gentle acceleration. / Use of neutral Remember. that there is no need to ^ove the gear lever into'Neutral'when stationary in traffic, even for many minutes. No wear is taking place; in fact more wear will take place if you put it into ’Neutral' then back into 'Drive' when you are ready to move off. You may find additional information on this in the vehicle handbook. Most gearboxes will automatically select first gear when your vehicle stops in anticipation of your next movement 63  I Emergency Ambulance Response Driver's Handbook / / Figure 6.7 An example of the four positions of the selector lever: izf P; Park - prevents the vehicle from rolling away when stopped ; R: Reverse - only engage reverse gear when the vehicle is stationary N: Neutral - no power is transmitted from the engine to the drive wheels D: Drive - automatic drive uses all forward gears and a configuration of 1, 2, 3 and 4 for manual selection, or a plus and minus sign for upward and downward manual changes, allowing the vehicle to be driven like a clutchless manual vehicle. } Safety warning It is vitally important to remember that automatics do not have a clutch pedal, Depressing the footbrake with the left foot, in the mistaken belief that this is the clutch, can have disastrous consequences - particularly if the vehicle is being driven at speed or being followed too closely by another road user. Automatics should always be left in 'Park' {P} when not being driven. When carrying out a pre-driving check, 'selector in P' should be substituted for 'gear lever in neutral'. Manual gear select 1^ many instances the selector lever can remain in 'D' for ordinary driving, C uring response driving, or in situations where additional control is required, t len an advantage may be gained by selecting one of the vehicle's special 64  Automatic Gearboxes programmes. Each vehicle manufacturer may have different systems, but generally they fall into the following categories - note a vehicie may only be fitted with one of the options below; ► Lock down (or shift restrictions) ► Sport ► Manual selection. Lock down (or shift restrictions) This is an effective means of controlling an automatic gearbox while descending steep gradients, overtaking or negotiating a corner or roundabout to ensure vehicle stability. The number of lock down options (or restrictions) varies and depends on how many gears the vehicle has. The number of lock down options will always be less than the total number of gears present: a five-speed gearbox may have four lock down options, while a vehicle with four ^ gears may have three. Lock down 1 Lock down 1 is used on very steep downhill gradients, to utilise engine compression to help control speed and lessen the load on the brakes. The vehicle should be brought to a halt at the top of the slope before selecting lock down 1. In lock down 1 the vehicle is locked in first gear and will not change up to any oth ir gear. The selector should be moved back to 'Drive' when the descent h as been completed. Lock down 2 ;rhe second setting is used to control speed on descents in the same way as lock down 1. As the gear is higher in lock down 2, there is less engine compression. This option is suitable for fairly steep downhill gradients or negotiating corners - the selector will not change up to third or any higher gear. Other lock down positions Alternative lock down positions may be used to control the vehicle like a manual clutchless vehicle. In all cases, the maximum upshift will be f position selected, for example if lock down T A Woe hppn selected then the vehicle will utilise ail geafs up to and 65  I Driver's Handbook mergency Ambulance Response \ YOU might ofchoose a number to lock hazards, down a control9^^ the acTefeTa^t'o^^'HowLer, to improve the ,n a five- I It is essential to remember to move to utilise lock down has passed. Driving the selector back to Drive’ when the need a lock down option can overheat the automatic.. the vehicle for a prolonged period transmission fluid and cause m \ damage to the transmission system. Sport mode and 4x4-type vehicles, rather than The sport setting is more often fitted to car the gearbox will hold lower gears commercial vehicles. By selecting this option the gearbox may not need to for longer, allowing for brisker acceleration as change down a gear in order to accelerate at maximum power. rJ ="”-=HH"srS5HSr” technology and as such you set-up prior to use. Manual selection of the gears through the some vehicles may be fitted with a manual selection buttons. These system.s selected lever or steering wheel-mounted paddles or driving a manual \ :an be -. )n the approach to a steep downhill section, a )riorto descent, Likewise, you may choose to secure a lower gear prior to negotiating a corner. a„ cases,.cv.ng the selector lever are too high. when attention cannot be diverted from Practice is essential to allow accuracy the road ahead to check the indicator panel. 5 i  Automatic Gearboxes Remember! With both automatic and manual gearboxes, you must be travelling at the correct speed for the gear that you want to select manually. Secondary braking should be avoided, I Important characteristics of automatic gearboxes Creep If any selector position other than 'P' or 'N' is selected, and the footbrake or handbrake are not applied, then the vehicle will tend to creep forward or backward at low speed, even when pressure is not applied to the accelerator pedal. The rate of creep varies in response to the force of gravity. Consequently, creep will be greater on a downhill slope than an uphill slope, Creep can, and must, be controlled by using the footbrake. It is particularly useful when manoeuvringat low speeds or in slow moving traffic. Creep may not hold a vehicle still on a steep hill. In such cases the handbrake should be used. Run on Deceleration in a vehicle fitted with manual transmission is relatively 'Straightforward - releasing pressure on the accelerator pedal slows the 'engine and deceleration is achieved by means of^ngine compression. This is especially effective in lower gears. This is not the case in an automatic vehicle when driving with the selector set in the 'D' position. Releasing pressure on the accelerator will not result in a change down to a lower gear, nor is engine compression apparent. This is referred to as 'run on' and provides a driving sensation similar to 'coasting'. If the vehicle is travelling uphill, gravity will slow it down. If the vehicle is travelling downhill, however, the combined effects of run on and gravity will result in a progressive increase in speed. Steep downward slopes can produce an alarming sensation of losing control as gravity takes over and vehicle speed rises sharply. 6'  Emergency Ambulance Response Driver's Handbook The timely and judicious use of iock down or a manual selection will effectively prevent this potentially dangerous circumstance. When driving on level stretches of road, early relaxation of pressure on the accelerator will facilitate more effcient acceleration sense. Kick down This is a useful safety feature that should only be used when there is actual or potential danger. It provides short-term bursts of maximum acceleration, to escape from hazardous circumstances, without the need to move the selector lever. Apply the accelerator pedal downwards rapidly to the furthest limit of its travel. After a very brief interval the transmission will change down to the next lowest gear and rapid acceleration will ensue. Holding the pedal down may result in a further subsequent change down and yet more acceleration. You then have a mechanismto escape from danger by using maximum acceleration when this is appropriate. Relaxing pressure on the accelerator results in loss of acceleration and a change back up to a higher gear. Care must be taken when using kick down. Plan and look well ahead to ensure that the vehicle is not powered out of one dangerous situation and into another. 0 KEY TERMS S’- Creep - the tendency of an automatic vehicle to creep forwards or backwards at low speed, even when pressure is not applied to the accelerator Run on - the tendencyof an automaticvehicle not to reduce speed when pressure is no longer applied to the accelerator; the vehicle may even gain speed if travelling downhill. \ Kick down - a feature of automatic vehicles that allows you to accelerate suddenly, overriding the automatic selection of gears. Electric and hybrid vehicles Although most electric and hybrid vehicles are fitted with automatic gearboxes they do not all have the same features mentioned here. For example, they may not 'run on’ when the accelerator is released, due to energy recuperation. This may mean that you need additional training, guidance or instruction on operating them. In all cases you should ensure through a pre-driving check that you are familiar with their controls, and ensure that you have read the vehicle handbook. 8