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 Engine accelerates above throttle rpm
10-31-2015, 06:07 AM (This post was last modified: 10-31-2015 06:11 AM by neodemon.)
Post: #1
 neodemon Junior Member Posts: 3 Joined: Oct 2015
Engine accelerates above throttle rpm
Hello,this is my first post on this forum.

I'm trying to get driveline code out of CarDynamics to simulate clutch/throttle without using any physics (bullet). All car parameters are taken out of Audi TT .car file.

When im simulating CarDynamics with clutch = 0.9, and throttle = 0.3 engine is slowly going to rpm_limit. In reality throttle position(and driveline - when engine and driveline are coupled through clutch) determines max engine rpm(between start_rpm and rpm_limit).
Is it intended, or is it my fault? (I simpified ApplyWheelForces to just apply torqes calculated by CalculateDriveTorque)
11-02-2015, 07:17 AM
Post: #2
 NaN Posting Freak Posts: 1,985 Joined: Jan 2010
RE: Engine accelerates above throttle rpm
The throttle determines engine torque, as long as the total torque on the crankshaft is positive the engine will accelerate.
11-02-2015, 04:15 PM
Post: #3
 neodemon Junior Member Posts: 3 Joined: Oct 2015
RE: Engine accelerates above throttle rpm
(11-02-2015 07:17 AM)NaN Wrote: In order to view links, you must have to reply to this thread.The throttle determines engine torque, as long as the total torque on the crankshaft is positive the engine will accelerate.

So there must exist torque that opposes throttle torque in the way that makes engine stop accelerating(or deccelerating) when engine rpm reaches throttle rpm. Is this true?

By throttle rpm i mean:
throttle_rpm = engine_idle_rpm + (engine_limit_rpm - engine_idle_rpm) * throttle_position
11-03-2015, 12:26 PM
Post: #4
 NaN Posting Freak Posts: 1,985 Joined: Jan 2010
RE: Engine accelerates above throttle rpm
(11-02-2015 04:15 PM)neodemon Wrote: In order to view links, you must have to reply to this thread.
(11-02-2015 07:17 AM)NaN Wrote: In order to view links, you must have to reply to this thread.The throttle determines engine torque, as long as the total torque on the crankshaft is positive the engine will accelerate.

So there must exist torque that opposes throttle torque in the way that makes engine stop accelerating(or deccelerating) when engine rpm reaches throttle rpm. Is this true?

By throttle rpm i mean:
throttle_rpm = engine_idle_rpm + (engine_limit_rpm - engine_idle_rpm) * throttle_position

The opposing torque comes usually from the wheels (tire friction), translating engine torque into car forward motion. There is no such thing as throttle_rpm.
11-03-2015, 02:33 PM
Post: #5
 neodemon Junior Member Posts: 3 Joined: Oct 2015
RE: Engine accelerates above throttle rpm
(11-03-2015 12:26 PM)NaN Wrote: In order to view links, you must have to reply to this thread.The opposing torque comes usually from the wheels (tire friction), translating engine torque into car forward motion. There is no such thing as throttle_rpm.

It cant be from tire friction, throttle(or gas) => rpm relationship works on neutral gear too. According to torque curve if engine rpm is between idle and limit, then engine produces some torque. If it always have torque on neutral, then how can engine rotate at constant rpm (when gas pedal is in constant position)?
11-05-2015, 03:55 PM
Post: #6
 NaN Posting Freak Posts: 1,985 Joined: Jan 2010
RE: Engine accelerates above throttle rpm
(11-03-2015 02:33 PM)neodemon Wrote: In order to view links, you must have to reply to this thread.
(11-03-2015 12:26 PM)NaN Wrote: In order to view links, you must have to reply to this thread.The opposing torque comes usually from the wheels (tire friction), translating engine torque into car forward motion. There is no such thing as throttle_rpm.

It cant be from tire friction, throttle(or gas) => rpm relationship works on neutral gear too. According to torque curve if engine rpm is between idle and limit, then engine produces some torque. If it always have torque on neutral, then how can engine rotate at constant rpm (when gas pedal is in constant position)?

It depends on how complex you want your model to be.

The opposing torque in the neutral case is engine friction. You choose the throttle position so that combustion torque + friction torque = 0, which results in constant rpm. This throttle position depends on combustion and friction torque curves and your target rpm.

But as soon as you have an additional load (tires) your rpm will drop and you will have to adjust throttle to get it back, keep it constant.
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