Governor

A governor system for the fuel pump of an engine which drives a vehicle through a multi ratio gearbox includes an all speed governor. The governor characteristic in the intermediate speed range is modified by means responsive to the load on the vehicle and by means responsive to the transmission ratio of the gearbox.

This invention relates to a governor system for the fuel pump of an 
internal combustion engine which in use powers a road vehicle. For a road 
vehicle used for transporting goods for example an articulated vehicle, it 
is the usual practice to provide a so-called all-speed governor system 
since the characteristic provided by such a system is ideal for use when 
the vehicle is in a loaded state. In such a system the driver of the 
vehicle sets the required engine speed and the governor system within the 
power capability of the engine and any other restraints such as engine 
exhaust smoke level, adjusts the fuel supply to the engine so as to attain 
and maintain the required speed. 
The governor system will respond very quickly to changes in the required 
speed but the response of the vehicle will be much slower because of its 
loaded state. 
An alternative form of governor system is known as the two-speed system in 
which the governor system controls the maximum speed and the idling speed 
of the engine. The intermediate speeds are controlled by the vehicle 
driver since in this system, in the intermediate speed range adjustment of 
the throttle pedal adjusts directly the amount of fuel supplied to the 
engine. Such a system facilitates the control of the vehicle when it is in 
an unloaded state but since vehicles are in most cases loaded to their 
maximum extent the usual practice is to provide an all-speed governor 
system. 
If the vehicle is in an unloaded state for example if in the case of an 
articulated vehicle the tractor unit is uncoupled from the trailer, the 
vehicle becomes more difficult to control since if the required speed is 
increased, the governor system will react to increase the fuel supply to 
the engine to its maximum allowed level and will only start to reduce the 
level of fuel supply as the new required speed is attained. Similarly if 
the required speed is reduced the governor system will react to reduce the 
level of fuel supply to a low value and will only increase the level of 
fuel supply as the new required speed is attained. In its unladen state 
therefore the vehicle is difficult to control. 
GB 2069187B proposes a partial solution to the above problem by providing a 
sensor which is responsive to the loaded state of the vehicle. The signal 
from the sensor is utilised to modify the governor characteristic. This 
solution is not entirely satisfactory and the object of the present 
invention is to provide a governor system in an improved form. 
According to the invention a governor system for the fuel pump of an 
internal combustion engine which drives a road vehicle through a variable 
ratio transmission, includes a governor having an all-speed characteristic 
and includes first means responsive to the loaded state of the vehicle and 
second means responsive to the transmission ratio of the transmission, 
said first and second means acting to modify the response of the governor 
in the intermediate speed range.

Referring to FIG. 1 of the drawings there is shown the characteristic of an 
all-speed governor with engine torque being plotted against engine speed. 
The line 10 represents the maximum fuel line which during normal operation 
of the engine cannot be exceeded. The line 11 represents the idle pull-off 
curve, the normal idling speed of the engine being that corresponding to 
the point 12. The line 13 represents the maximum speed pull-off curve, the 
point 14 corresponding to the maximum permitted engine speed. The lines 15 
and 16 lying between the lines 12 and 13 represent different levels of 
demanded engine speed, the line 16 as indicated by the arrow, representing 
a higher demand than the line 15. 
Suppose for example that the engine is operating at point A in equilibrium 
that is to say just sufficient fuel is being supplied to the engine to 
provide sufficient torque to maintain the steady speed of the engine. In 
the event that the operator of the vehicle increases the demand to attain 
an increased speed represented by the point B, the torque provided by the 
engine will increase in more or less a step wise manner to the point C. 
This is because in response to the increased demand, the governor system 
will move the fuel control member of the fuel pump to a position to 
provide the maximum fuel. With the increased torque available the engine 
speed will increase to the point D and in the particular example, there 
will be a slight increase in the amount of fuel supplied to the engine. As 
soon as point D is reached whilst there will be an increase in engine 
speed, the torque developed by the engine will in fact reduce this being 
occasioned by movement of the control member of the fuel pump to reduce 
the amount of fuel supplied to the engine. Point B represents a new 
equilibrium position which is established at the new desired speed with 
the engine torque increased to maintain that speed. It will be noted from 
FIG. 1 that there is a substantial increase in the torque delivered by the 
engine and this increase in torque results in an increase in torque at the 
driving wheels of the vehicle. The actual torque available at the driving 
wheels of the vehicle depends upon the gear ratio of the transmission of 
the vehicle and as a gear is selected which results in a higher engine 
speed for a given road-speed of the vehicle there will be an increase in 
the torque multiplication. It is therefore more difficult to control the 
vehicle as the gear ratio is changed in the direction to increase the 
engine speed for a given road speed. The effect is made worse if the 
vehicle is unladen. It is therefore proposed to modify the governor 
characteristics in accordance with the gear ratio selected and in 
accordance with the state of load of the vehicle. 
FIG. 2 shows modified governor characteristics which show the lines 15A and 
16A having a greater reverse slope. Starting at the point A on line 15A 
when the driver requires to increase the speed to that corresponding to 
point B, depression of the throttle pedal will result in an increase in 
the amount of fuel supplied to the engine but the actual increase will be 
limited to that which corresponds to point E lying on the line 16A. The 
increase in engine torque is therefore substantially less than that which 
is shown in FIG. 1 and the greater the reverse slope, the smaller the 
increase in torque which occurs. Thus the increase in torque at the 
driving wheels of the vehicle is reduced and this facilitates control of 
the vehicle. 
The value of the reverse slope is ideally chosen such that a constant 
vehicle acceleration results from a uniform increase in demand, this being 
a direct function of available tractive effort and an inverse function of 
the vehicle mass according to Newtons first law. In practice the system is 
likely to limit acceleration to acceptable levels in operating regions 
where low gear ratios and/or low vehicle weight exist with full available 
engine power being transmitted where this does not inhibit vehicle control 
or ride comfort. Ideally a progressive load sensor is used for the 
derivation of vehicle weight but again this can be comprised practically 
by sensors which give an indication of the loaded state of the vehicle or 
even by switch inputs under the control of the vehicle driver. 
FIG. 3 shows the layout of the governor system and its connection to a fuel 
control actuator 17 associated with a fuel pump 9 supplying fuel to an 
engine 8. The engine is connected through a multi-ratio gearbox 7 to the 
powered road wheels of the vehicle. The governor generally indicated at 18 
includes a first section 19 which controls the supply of fuel to the 
engine 9 below the normal idling speed. Section 20 controls the supply of 
fuel as the engine speed approaches its maximum speed and section 21 
determines the supply of fuel to the engine in the intermediate speed 
range. Each section is supplied with signals corresponding to the actual 
engine speed and the demanded engine speed, these signals being provided 
by circuit means 22. The outputs of the portions 19, 20 and 21 of the 
governor system pass to a control circuit 23 which combines the outputs 
and controls the operation of a power circuit 24 the output of which is 
connected to the actuator 17. 
Besides the actual and demanded speeds, the portion 21 also receives 
signals from sensors 25, 26, sensor 25 being arranged to provide a signal 
indicative of the loaded state of the vehicle and sensor 26 being arranged 
to provide an indication of the selected gear ratio of the box 7. The 
outputs of the sensors 25 and 26 are passed to a decoder 27 which supplies 
a signal to the portion 21 of the governor to determine the slope of the 
lines 15A and 16A, it being appreciated that these two lines are merely 
two examples of a large number of lines which can be constructed and lie 
between the lines 12 and 13.