OT: Why do cars have Tachometers?

Why would you put all those smarts onto a manual gear box?

Short answer, you wouldn't.

Easy enough to simply hook into the ECU for mappings that are economical and light the green light.

RPM per fuel input would probably be an indicator.

But the car will already have sensors for road speed (speedometer), engine speed (tachometer), throttle pedal position (to request the ECU to delivery more fuel if it makes sense to do so). The only thing that wouldn't be measured would be the engine load, which would require some form of strain gauge.

RPM per fuel input is probably a good indicator, as you say. But that on its own wouldn't detect the engine labouring because it is in too low a gear for the engine speed and the gradient - unless the ECU detects that the accelerator is requesting too much fuel, which is a symptom of the drive trying to accelerate (or even maintain a constant speed) when the engine can't deliver enough torque to the wheels.

Our Honda CRV is occasionally very optimistic about how much torque the engine can deliver: it sometimes recommends changing up when doing so causes the engine to labour and the car to reduce speed.

Well, both of the two I've been driving (one diesel, one petrol) tell you what gear you should be in. And allow higher engine speeds at higher throttle settings. It's not just a vacuum gauge - they just tell you to drive slowly.

I find I rarely have the "in too high a gear" light come on.

Andy

In article snipped-for-privacy@4ax.com, Scott snipped-for-privacy@gefion.myzen.co.uk> writes

Once upon a time they were a luxury item. Only sporty cars had them. Incredibly we all managed to drive quite well without them.

You might have done but there are still plenty of people on the road today who don't make anything like the full use (typical rev range) of their engine, who might learn something from one if shown how to use it.

Even I will rarely make *full* use of the rev range because I don't need to but I do typically use the range going up though the gears when say merging with some fast moving / motorway traffic that I might when cruising at speed.

Some short shift just past tickover into top and then expect the engine to pull them from the same low revs up to motorway speeds / revs?

Maybe just the reverse of a rev limiter light might be useful for them that helps them get up to speed when joining a motorway ... and forces then to stay on the slip lane till near the end, not let them dive across the crosshatching at 30mph into 70 mph traffic.

Cheers, T i m

I find I use my rev counter to confirm by how much I need to increase/decrease the engine revs when changing up or down, so as to give a smoother gearchange. With a modern engine being fairly quiet, it is surprisingly difficult to tell by engine note alone. It is also useful to know when to change up when accelerating hard (so as not to over-rev the engine).

But they are a bit of a luxury item. I could (and did) manage perfectly well without them on my older cars. If a rev counter is there., I will use it; if it's not, I won't miss it too much.

At least rev counters are now calibrated as 1, 2, 3 x1000 rpm, rather than the older 10, 20, 30 x100 rpm. The latter gave two gauges which has similar numbers, which led to occasional confusion in an unfamiliar car, and also offended my scientific/engineering background where large (or small) numbers are conventionally expressed as being multiplied by powers of 1000 (ie 1-999 x 10^-6, 1-999 x 10^-3, 1-999, 1-999 x 10^3. 1-999 x 10^6 etc).

There is the opposite sort of driver (usually elderly) who revs the engine almost to the limiter when manoeuvring in a car park, and then just kisses the clutch to control the speed. One slip of the clutch and you've hit something. With my diesel-engined car, I can usually reverse into/out of a car parking space without my foot on the accelerator, letting the engine just tick over; likewise when crawling along in a queue of traffic: engine barely above idling in either 1st or 2nd according to speed needed.

Labourng is a high throttle input and a low RPM essentially. Very easy for the ECU as it leads to high fuel low RPM.

Crap software. Like I said mostly its a virtue signalling light.

Yup. As mentioned elsewhere my mate used to look after the vehicles of such a driver and was doing regular clutch changes for her (plus loads of bodywork).

I *can* do that with my petrol engined car but it's not quite torquy enough to do effectively.

Yes, I can and do that in long traffic queues and in many cases it can set others doing so and prevents that stop-start shuffle thing.

The problem is lane jumpers who will gain one place by jumping into the game you left.

As always, it only take a selfish / stupid minority to spoil it for everyone.

Cheers, T i m

You mean you use the correct gear. Does that really require a rev counter?

The best older non electronic autos used engine vacuum to determine when to change gear - as well as road speed and engine RPM, obviously.

Maker's ECUs usually have some form of air flow meter. Knowing the throttle position isn't actually as important as you might think.

Ages ago, had a mate who learned to drive rather later in life than most, in his 30s. After becoming successful in business. And his first car was an E-Type Jaguar. A manual, as most were then. And it terrified him. The only way he could keep it under control was by starting off in a very high gear - usually third, and slipping the clutch. Which was lucky to last

When I had a Primera 2.2 Diesel, I once tried driving it without the accelerator - I could get up to just under 50mph in 6th gear! Although the acceleration was slow, it was fast enough not to be unusable like that and certainly would have been able to get me home if the accelerator broke.

These days I have a Zafira 1.8 petrol and find that 2nd gear and feet off gives a perfect 10mph for the car park at work.

SteveW

Somehow my car (Peugeot 308 diesel) is still on its original clutch after

I can well imagine that a powerful car like an E-Type would be rather difficult to set off gently, without spinning the wheels. Not really a good first car for someone who's just passed his test ;-)

I thought it was the oil pressure in the torque converter.

I drove it often. No problem at all, except for a pretty heavy clutch. And the performance nothing special today. They were extremely heavy cars.

The line pressure is controlled in a number of ways.

In article <qv4868$tm$ snipped-for-privacy@dont-email.me, NY snipped-for-privacy@privacy.invalid writes

My VW Transporter stalls very easily unlike my Defender which will take quite a bit of abuse.