Thread: 4BD1 injector pump question

Originally Posted by wovenrovings

Thanks for all the info everyone, specially bush 65 with all those pics.

So to check my understanding: the the sensor lever follows the movement of the rack until it contacts the torque cam or the max fuel lever hits its stop.

The bit i am not sure about is if the sensor lever is solidly connected to the max fuel lever.
But now i know why the max fuel lever doesn't move much from an idle.


Cheers,
Dan.

The governor has to control the fuel delivery rate to try and give the engine speed that the driver is demanding via the accelerator pedal/linkage. It also has to prevent engine over speed, etc.

As load increases/decreases (e.g. up/down hills) the governor has to increase/decrease the fuel deliver by moving the control rack.

As the accelerator linkage is moved for higher/lower speed, the governor has to increase/decrease fuel delivery.

As the engine speed reaches the maximum set speed, the governor has to reduce fuel delivery.

The complexity in the governor is there because of all of the variables.

The governor on our 4BD1's (and later mechanical controlled Isuzu truck engines) is the Bosch RLD type. Other governors are used for different applications - for example a motor generator set has to maintain constant speed (to keep the AC frequency at 50Hz, or whatever is required) as the generator current demand (load on engine) changes. Bosch have superseded the RLD governor with the RQV for mechanical (not computer controlled) applications.

The sensor lever and torque cam is the mechanism that the RLD governor uses to limit the control rack travel in the increasing fuel direction of rack travel. The shape of the torque cam allows the limit stop position to change to suit whatever the engine revs are.

The sensor lever is not solidly connected to the "maximum fuel lever" (full load set lever). Both the sensor lever and full load set lever pivot from the U shaped lever.

The sensor lever follows the movement of the control rack and prevents further travel of control rack, in the increasing fuel direction, when the sensor lever contacts the torque cam.

Rotation of the U shaped lever changes the pivot point of the sensor lever, thereby changing how far the control rack can travel. This is the mechanism that the governor uses to control fuel delivery as the engine load increases/decreases.

And the full load set lever and full load set bolt on the side of the governor limit how far the U shaped lever can rotate. As the load increases (going up a hill or accelerating harder for example) the U shaped lever rotates to move the pivot point of the sensor lever, so the fuel delivery increases. Once the full load set lever hits the full load set bolt, the U shaped lever can not rotate further.

If you adjust the full load set bolt, to allow the U shaped lever to rotate further, you increase the power and torque that the engine can produce - as long as the engine can get enough air to burn the extra fuel and not just blow black smoke and increase the exhaust gas temperature.

Ok thanks, so that makes it a complex little setup. That has answered my orginal question.

But i'm curious, what makes the U shape lever move? does is have a connection to the governor?

That book you got the pictures out of for the injector pump, what is it called?

Thanks,
Dan.

Originally Posted by wovenrovings

Ok thanks, so that makes it a complex little setup. That has answered my orginal question.

But i'm curious, what makes the U shape lever move? does is have a connection to the governor?

That book you got the pictures out of for the injector pump, what is it called?

Thanks,
Dan.

The reaction at the pivot of the sensor lever apposing the return spring at the full load set lever and the cancel spring between the full load set lever and the U shaped lever.

The pics came out of an Isuzu injection pump service manual, INJ.SE.011

Edit: BTW, the bottom part of the sensor lever is shaped like a beak. When the engine is stopped, if you depress the accelerator fully, this beak moves under the notch at the bottom of the torque cam. This is the fuel enrichment for cold starting. When the engine starts and you release the accelerator, the governor moves the torque cam and the sensor lever contacts it normally.