Motor vehicle hill holder system

Provided is a hill holder system operative to prevent a vehicle such as a truck having a fluid operated brake system from rolling backward down an incline or to assist an operator in braking when descending an incline. The system utilizes a control signal (C) provided by a central processing unit (10) operative to instruct a brake control valve (22) to close the brake balve exhaust port(s) (27) to maintain the brakes in an engaged condition whenever a selected speed condition such as vehicle ground speed is below a predetermined value. In other embodiments, selected vehicle drive train conditions such as either or both throttle and clutch position are processed in combination with the selected speed signal to effect braking in the manner desired.

INTRODUCTION 
This invention relates generally to a motor vehicle hill holder system and 
more particularly to a system that in one embodiment is operative to 
maintain the motor vehicle brakes in an engaged condition so long as a 
selected speed condition such as vehicle land speed is below a 
predetermined value and in another embodiment combines the selected speed 
condition with one or more drive train conditions such as throttle and 
clutch positions to control actuation of the brakes. This invention is 
partially described and may be used in conjunction with my copending 
application Ser. No. 600,657 filed Oct. 22, 1990 and entitled "Automatic 
Mechanical Transmission Start Control System". 
BACKGROUND OF THE INVENTION 
A variety of hill holder systems have been proposed in the past to 
automatically brake a vehicle descending a hill or to prevent a vehicle 
from rolling backwards while ascending a hill when the vehicle is 
traveling below some predetermined minimum speed value. 
Such can be of particular advantage to the vehicle driver in instances 
where the vehicle is a truck carrying a heavy load. 
One example of a motor vehicle hill holding system is disclosed in U.S. 
Pat. No. 4,582,184, the disclosure of which is incorporated herein by 
reference. The device disclosed in this patent is operative to maintain 
the brakes in an engaged condition when the clutch pedal is depressed and 
the vehicle comes to a stop on an incline by means of a linkage connection 
between the clutch and brake pedal. 
Another example of a motor vehicle is disclosed in U.S. Pat. No. 4,650,046, 
the disclosure of which is incorporated herein by reference. In this 
patent, the hill holder device includes a undirectional sprag clutch that, 
when actuated, permits the drive shaft to rotate in only one direction 
thus preventing it from rotating in an opposite direction in the event 
that the vehicle begins to roll backwards down an incline. 
Yet another example of a motor vehicle hill holding system is disclosed in 
U.S. Pat. No. 4,867,291, the disclosure of which is incorporated herein by 
reference. Here, a sprag clutch is employed to limit transmission 
countershaft rotation to only one direction which again operates to 
prevent the vehicle from rolling in the opposite direction as previously 
described. 
Although the above described devices may be used to advantage they all 
employ complicated clutch or linkage mechanisms that are expensive to 
install and maintain. 
In contrast to the above described prior art, the present invention employs 
a relatively simple fluid control valve arrangement that is responsive to 
a control signal derived from a selected speed condition signal alone or 
in combination with a selected drive train condition such as a throttle 
position and/or clutch position so as to cause the brakes to automatically 
engage when the control signal is below a predetermined value. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide a motor vehicle 
hill holder system. 
It is another object of this invention to provide a motor vehicle hill 
holder system that is simple in operation and inexpensive to install and 
to maintain. 
It is yet another object of this invention to provide a motor vehicle hill 
holder system that is operative to maintain the brakes in an engaged 
condition in response to a control signal derived from a selected speed 
condition signal or from a combination of the speed condition signal and a 
selected drive train condition such as throttle position and/or clutch 
position.

DESCRIPTION OF SOME PREFERRED EMBODIMENT 
In FIG. 1, an embodiment of the hill holder system is applied to a motor 
vehicle driven by an internal combustion engine 2. The speed of engine 2 
is controlled by a throttle 18 whose position is sensed by sensor 20. 
Engine 2 is operatively connected to the vehicle's transmission 4 by 
clutch 6. Engine 2 is operative to rotate drive shaft 8 when clutched to 
transmission 4 and the rotary speed and direction of shaft 8 is governed 
by the gear combinations selected by selector 12. 
The hill holder system of the invention includes at least one speed sensor 
operative to sense and provide a signal indicative of a selected speed 
condition such as one or more of ground speed, engine speed, change in 
ground speed, and change in engine speed. Ground speed can be deduced for 
example from either transmission input speed sensor 14 or a transmission 
output speed sensor 16 and engine speed can for example, be sensed by 
monitoring the main drive shaft RPM such as by engine speed sensor 19 
diagrammatrically shown in FIG. 1. 
The hill holder system of the invention preferably includes a brake 
position sensor such as referenced by numeral 23 in FIG. 1 that is 
operative to provide a signal indicating whether the vehicle brakes 25 are 
in an engaged or disengaged condition. 
The hill holder system of the invention also preferably includes a clutch 
position sensor 17 operative to provide a clutch position signal 
indicating whether the clutch is in an engaged or disengaged condition. 
Brakes 25 are operated by pressurized fluid such as air or a suitable 
liquid brake fluid that is conveyed under pressure from brake valve 24 to 
respective wheel brake cylinders (not shown) that are mechanically linked 
to the brakes and operative to move the brakes into engagement when 
pressurized as is well known to those skilled in the art of vehicle brake 
design. 
As shown in FIGS. 2 and 3, brake valve 24 has at least one exhaust port 27 
that is normally closed when the brakes are engaged and normally open when 
the brakes are disengaged. Brake valve 24 receives pressurized fluid from 
a pressurized fluid supply 30 and is operative to enable the pressurized 
fluid to be delivered to the brake cylinders when pedal 26 is pressed in a 
clockwise direction as viewed in FIGS. 2 and 3 whilst exhaust port 27 is 
closed. When brake pedal 26 is released, exhaust port 27 opens to enable 
fluid pressure to decrease to ambient which in turn decreases pressure in 
the wheel brake cylinders to ambient enabling release of the brakes 
characteristically by return spring action, as is well known to those 
skilled in the art of vehicle wheel brake design. 
In FIG. 2, the system of the present invention employs a control valve 22 
that is operatively connected to exhaust port 27 and is operative to 
control whether pressurized fluid is able to exhaust from port 27 in 
response to a control signal "C" hereinafter described. 
Control signal C is an output signal provided by control processing unit 10 
shown in FIG. 1. Control signal C is preferably an electrical signal that 
is delivered to brake control valve 22. Control signal C is a signal that 
in one embodiment of the invention is a function of speed derived from a 
selected speed condition such as vehicle ground speed from either 
transmission input speed 14 or transmission output speed 16 as previously 
described. When control signal C is based upon a ground speed it may also 
be derived from other sources on the vehicle that in one way or another or 
correlatable to ground speed such as directly from the speedometer itself 
or from tire RPM. 
The speed condition signal can be sensed from a change in ground and/or 
engine speed as well as from ground and/or engine speed where such is 
desired. A change in ground speed and/or engine RPM is characteristically 
indicative of increased load while undergoing acceleration which the 
system of the invention can then employ to automatically release the 
brakes while undergoing an acceleration and vice versa while undergoing a 
deceleration so as to automatically apply the brakes when the selected 
speed signal is below the predetermined value. 
Brake control valve 22 is preferably an electrical solenoid actuated valve 
that receives control signal C and is operative to close exhaust port 27 
of valve 24 when, for example, the vehicle speed is below a predetermined 
value such as 3 miles per hour. Brake valve 24 receives pressurized fluid 
from supply 30 and, while exhaust port 27 remains closed, pressure is 
unable to bleed off of the brake cylinders and the brakes remain in the 
engaged condition regardless of whether the operator releases foot pedal 
26 shown in FIGS. 2 and 3. 
When, for example, vehicle ground speed is greater than a predetermined 
value, control signal C instructs control valve 22 to open exhaust port 27 
enabling pressure to bleed from the brake cylinders causing the brakes to 
release enabling the operator to accelerate by depressing or actuating the 
throttle which itself can be used to advantage as shown in FIG. 1, where a 
throttle position sensor 20 is employed to provide processing unit 10 with 
information concerning the position of throttle 18 in combination with a 
selected speed condition alone and/or in combination with clutch position 
as previously described. When throttle 18 is pressed by an operator, unit 
10 processes the information in combination with the selected speed 
condition and sends a control signal C instructing control valve 22 to 
open so as to enable pressure bleed off from brake valve 24 for release of 
brake 25. 
When the hill holder system of the invention includes a change in one or 
more selected drive train conditions, such as clutch and or throttle 
positions, in combination with the selected speed condition signal as 
information to be processed by information processing unit (10), the 
system is then effective such that control signal C is operative to 
instruct control valve 22 to open exhaust port 27 of brake valve 24 to 
disengage the brakes when the speed condition signal has increased 
sufficiently to reach the predetermined value such as when the throttle is 
advanced or the clutch is engaged while the speed signal is below the 
predetermined value. 
FIG. 3 shows a variation of the system of the invention in which a control 
valve 28 is operative to receive control signal C and close exhaust port 
27 of brake valve 24 when, for example, vehicle ground speed is below a 
predetermined value so as to keep the brakes engaged as previously 
described. Control valve 28 differs from control valve 22 of FIG. 2 in 
that it includes an additional input port 29 connected to a controlled 
fluid pressure supply source 32. Control signal C is operative to effect 
fluid communication between valve 28 and source 32 to enable valve 28 to 
receive controlled fluid pressure from fluid supply 32 and to control the 
rate at which control valve 28 is able to open exhaust port 27 of brake 
valve 24. For example control valve 28 may be operative to drive a piston 
or the like to open and close a port that in turn enables exhaust to pass 
from exhaust port 27 or stop it, as the case may be. Fluid supply 32 may, 
for example, be is exposed to the opposite side of the cylinder head and 
operate to control the rate at which the exhaust port is opened which in 
turn controls the rate at which the brakes are released. 
Thus, many variations of selected speed conditions alone or in combination 
with selected drive train conditions such as either or both throttle and 
clutch position may be used to provide desired information for processing 
by the control processing unit to provide the output signal C for 
operating the brakes under hill holding circumstances. Thus, for example, 
control signal C can be used to open the brake valve exhaust port to 
enable manual braking on operator when the selected speed condition signal 
is above a predetermined value. Likewise, control signal C may be employed 
to change a condition of the exhaust port such as hereinbefore described 
with respect to FIG. 3 so that the brakes are maintained in a engaged 
condition, including the level of engagement, so long as the speed signal 
remains below the predetermined value. Even further, control signal C is 
operative to open the exhaust port to disengage the brakes when the speed 
signal has increased sufficiently to reach the predetermined value. 
In addition to the above, drive train conditions such as throttle position 
and/or clutch position signals may be processed in combination with the 
speed condition signal to effect engagement or disengagement of the brakes 
in the manner desired such as where the brakes are caused to disengage 
when the throttle is advanced and or the clutch is engaged even through 
the speed condition signal is below the predetermined value. 
Thus, the system of the invention employs a control valve responsive to a 
control signal that is operative to open and close the brake valve exhaust 
port(s) (may be more than one) according to whether the selected speed 
condition is above or below a predetermined value. Once below that value, 
the control valve operates to close the brake exhaust port(s) and maintain 
the brakes in an engaged condition to prevent the vehicle from rolling 
backward down an incline or to automatically brake the vehicle when 
descending an incline. In addition, combinations of selected drive train 
conditions such as throttle and clutch position may be processed with the 
selected speed condition signal to effect braking in the manner desired 
and the hill holder system of the invention does not in any manner prevent 
an operator from pressing on the brakes at anytime to override the system 
when desired.