GB1567032A - Hydraulic load sensing valve units - Google Patents

Description

(54) IMPROVEMENTS IN HYDRAULIC LOAD SENSING VALVE UNITS (71) We, CLAYTON DEWANDRE COMPANY LIMITED, a British Company of, Titanic Works, Lincoln, LN5 7JL do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to valve units used in hydraulic braking systems of motor vehicles to regulate braking pressure in accordance with vehicle load.Such valve units are commonly known as and will be referred to hereafter as load sensing valve units the invention being concerned with units of the kind in which input of pressure fluid from a master cylinder or brake control valve displaces an input piston which, through lever mechanism and a balancing or output piston, actuates a valve member to deliver a output of pressure fluid for actuating the brake cylinders, the effective leverage of said mechanism and thereby the ratio of input to output pressures being variable in dependence of vehicle load.

The object of the present invention is to provide an improved valve unit of the above kind which is of compact form and simplified shape so facilitating installation on a vehicle.

According to the invention in a load sensing valve of the kind above-mentioned, the input and output pistons are co-axially disposed, the lever mechanism comprising a lever mounted on a fixed pivot and bearing on the output piston and a stirrup member having operative connection with the input piston and carrying a roller bearing on the lever, and said stirrup member being displaceable under variations in vehicle load such as to displace the point of contact of said roller along the lever.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a side elevation of the valve unit; Figure 2 is an axial sectional view through the valve unit; and Figure 3 is another sectional view taken at right angles to Figure 2 and on the line III-III thereof.

The valve unit shown comprises a valve body or housing 1 bored to define two co-axial vertical cylinders 2, 3 separated by a valve chamber 4, said valve chamber including a seating 5 for a spring-loaded ball valve member 6 which when moved off the seating interconnects the upper cylinder 2 and the valve chamber 4. Laterally disposed input and output ports 7, 8 respectively in the valve body are connected by passageways to the valve chamber and upper cylinder respectively, the valve chamber being in permanent communication with the lower cylinder 3. An output piston 9 in the upper cylinder 2 includes a stem 10 on its lower side operable to move the ball valve 6 off its seating, the upper side of said piston being engaged by a pad 11 provided on a lever 12 intermediate its ends and which lever is fulcrumed at one end on a fixed pivot 13.

An input piston 14 in the lower cylinder 3 and coaxial with the input piston 9 is urged in a downward direction by a spring 15 and has at its lower end a ball and socket or equivalent pivotal connection 16 with the lower end of a 'U'-shaped stirrup member 17, the upper end of which carries a spindle 18 supporting a thrust roller 19 which rides upon the upper side of the lever 12. A shaft 20 journaled in a side wall of the valve body carries fast on its inner end an arm 21 which at its free end includes a bent over portion 21a embracing an arm of the stirrup 17 such that oscillation of said shaft rocks the stirrup about the ball and socket connection to move the point of contact between the roller 19 and lever 12 along said lever.In use, the load sensing valve unit is mounted on the vehicle frame whilst a further arm 22 secured to the outer end of said shaft is connected to an unsprung part of the vehicle, whereby the said arm and thus the stirrup is oscillated under changes of vehicle load. The valve unit operates as follows: When pressure fluid from the brake line is admitted to the input port 7 it enters the lower cylinder 3 and depresses the piston 14.

This piston movement is transmitted through the stirrup 17 and thrust roller 19 to the lever 12 which in turn is oscillated to depress the upper piston 9. The stem 10 of this piston thereby moves the ball valve 6 off its seating 5 so allowing the pressure fluid to flow to the output port 8 and so to the brakes. The valve unit has a "follow-up" action, that is, when a desired pressure has been transmitted to the brakes that pressure acting on the underside of the upper piston 9 tends to raise this piston and thereby the lever 12 whereby the valve unit assumes a lap condition to hold the brakes applied at the prevailing pressure until action is taken to release the brakes.With the construction above described it will be appreciated that the pressure at which the valve unit assumes a lap condition relative to the supply of input pressure will depend upon the relative effective areas of the two pistons 9, 14 and the effective lengths of the lever arms, that is, the distances from the points of contact of the lever 12 with the upper piston 9 and with the thrust roller 19 to the lever pivot, and thus the movement of the thrust roller along the lever under changing vehicle loads will result in an appropriate apportioning of the braking pressure.In one practical embodiment incorporating an upper piston of slightly larger diameter than the lower piston, the valve unit in one limit position of the stirrup when the thrust roller is located closely adjacent the lever pivot results in a 1:1 ratio of input to output, whilst movement of the roller towards the free end of the lever progressively varies said rate up to 1:4 although such a wide range of adjustment will not always be required. If desired, a pointer 23 may be secured to the shaft/arm assembly 20, 21 to co-operate with a dial 24 as shown in Figure 1 and provide a visual indication of the setting of the valve unit.

WHAT WE CLAIM IS: 1. A load sensing valve unit of the kind referred to, wherein the input and output pistons are co-axially disposed, the lever mechanism comprising a lever mounted on a fixed pivot and bearing on the output piston and a stirrup member having operative connection with the input piston and carrying a roller bearing on the lever, and said stirrup member being displaceable under variations in vehicle load such as to displace the point of contact of said roller along the lever.

2. A load sensing valve unit as claimed in Claim 1, induding a housing defining two cylinders within which are respectively disposed said input and output pistons and which are located at opposite sides of a valve chamber, a passage-way connecting an input port to the valve chamber and a further passage-way connecting an output port to the output piston cylinder, the input piston cylinder being in permanent communication with the valve chamber whilst a connection between the valve chamber and the output piston cylinder is controlled by the valve member which is movable from its seating by displacement of the output piston.

3. A load sensing valve unit as claimed in Claim 2, wherein said valve unit is adapted for mounting on the vehicle frame and journaled in the valve unit housing is a shaft to which is secured an arm for connection to an unsprung part of the vehicle, said shaft also supporting a further arm having a connection with the stirrup member such that oscillation of the shaft under variations of vehicle load also oscillates the stirrup member to displace the roller carried thereby along said lever.

4. A load sensing valve unit of the kind referred to, constructed and adapted to operate substantially as herein described with reference to the accompanying draw ings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. vehicle frame whilst a further arm 22 secured to the outer end of said shaft is connected to an unsprung part of the vehicle, whereby the said arm and thus the stirrup is oscillated under changes of vehicle load. The valve unit operates as follows: When pressure fluid from the brake line is admitted to the input port 7 it enters the lower cylinder 3 and depresses the piston 14. This piston movement is transmitted through the stirrup 17 and thrust roller 19 to the lever 12 which in turn is oscillated to depress the upper piston 9. The stem 10 of this piston thereby moves the ball valve 6 off its seating 5 so allowing the pressure fluid to flow to the output port 8 and so to the brakes. The valve unit has a "follow-up" action, that is, when a desired pressure has been transmitted to the brakes that pressure acting on the underside of the upper piston 9 tends to raise this piston and thereby the lever 12 whereby the valve unit assumes a lap condition to hold the brakes applied at the prevailing pressure until action is taken to release the brakes.With the construction above described it will be appreciated that the pressure at which the valve unit assumes a lap condition relative to the supply of input pressure will depend upon the relative effective areas of the two pistons 9, 14 and the effective lengths of the lever arms, that is, the distances from the points of contact of the lever 12 with the upper piston 9 and with the thrust roller 19 to the lever pivot, and thus the movement of the thrust roller along the lever under changing vehicle loads will result in an appropriate apportioning of the braking pressure.In one practical embodiment incorporating an upper piston of slightly larger diameter than the lower piston, the valve unit in one limit position of the stirrup when the thrust roller is located closely adjacent the lever pivot results in a 1:1 ratio of input to output, whilst movement of the roller towards the free end of the lever progressively varies said rate up to 1:4 although such a wide range of adjustment will not always be required. If desired, a pointer 23 may be secured to the shaft/arm assembly 20, 21 to co-operate with a dial 24 as shown in Figure 1 and provide a visual indication of the setting of the valve unit. WHAT WE CLAIM IS:

1. A load sensing valve unit of the kind referred to, wherein the input and output pistons are co-axially disposed, the lever mechanism comprising a lever mounted on a fixed pivot and bearing on the output piston and a stirrup member having operative connection with the input piston and carrying a roller bearing on the lever, and said stirrup member being displaceable under variations in vehicle load such as to displace the point of contact of said roller along the lever.

2. A load sensing valve unit as claimed in Claim 1, induding a housing defining two cylinders within which are respectively disposed said input and output pistons and which are located at opposite sides of a valve chamber, a passage-way connecting an input port to the valve chamber and a further passage-way connecting an output port to the output piston cylinder, the input piston cylinder being in permanent communication with the valve chamber whilst a connection between the valve chamber and the output piston cylinder is controlled by the valve member which is movable from its seating by displacement of the output piston.

3. A load sensing valve unit as claimed in Claim 2, wherein said valve unit is adapted for mounting on the vehicle frame and journaled in the valve unit housing is a shaft to which is secured an arm for connection to an unsprung part of the vehicle, said shaft also supporting a further arm having a connection with the stirrup member such that oscillation of the shaft under variations of vehicle load also oscillates the stirrup member to displace the roller carried thereby along said lever.

4. A load sensing valve unit of the kind referred to, constructed and adapted to operate substantially as herein described with reference to the accompanying draw ings.