Master cylinder

A combined master cylinder and dump valve includes a piston slideable within a body bore that defines a master cylinder for pressurizing a brake port. The piston includes a piston seal for isolating a pressure port from a tank port, a piston bore, a first piston hole set for hydraulically connecting the pressure port to the piston bore and a second piston hole set for hydraulically connecting the piston bore to the tank port. A plunger slideably received in the piston bore has a plunger hole set for selectively connecting the first piston hole set with a plunger bore, and a plunger seal arrangement for selectively isolating the first piston hole set from the plunger bore. The plunger bore is hydraulically connected to the piston bore.

REFERENCE TO RELATED APPLICATION

This application claims priority to Great Britain Patent Application GB 0321389.9 filed on Sep. 12, 2003.

TECHNICAL FIELD

The present invention relates generally to combined master cylinder and dump valves and also to a method of manufacturing such valves. The invention also relates to a method of manufacturing a combined master cylinder and booster.

BACKGROUND OF THE INVENTION

Certain vehicles, such as bulldozers, use a hydrostatic drive system. Typically, an engine-driven hydraulic pump provides a flow of pressurized hydraulic fluid to a hydraulic motor. The hydraulic motor is coupled to wheels (or tracks) of the vehicle. Thus, by driving the hydraulic motor, it is possible to maneuver the vehicle. The vehicle includes brakes, and to prevent overheating of the brakes, pressurized flow of the hydraulic fluid to the hydraulic motor should substantially cease prior to the brakes being applied.

It is known to provide a “dump valve” between the engine-driven hydraulic pump and the hydraulic motor. Opening of the dump valve causes the hydraulic pump and the hydraulic motor to vent to a tank, thereby ceasing driving input to the vehicle wheels. Once the dump valve is open, the brakes are then applied. In this way, the brakes are only required to slow the vehicle and do not act against any driving force of the hydraulic pump and the hydraulic motor.

Furthermore, certain other vehicles, such as agricultural tractors that do not typically use a hydrostatic drive system, are known to use a combined brake master cylinder and booster. Vehicles that use hydrostatic drive systems, such as the bulldozers discussed above, do not use a combined brake master cylinder and booster. Similarly, vehicles that use a combined brake master cylinder and booster do not have hydrostatic drive systems.

In combined brake master cylinder and boosters, brake pedal effort applied via a push rod is increased (or boosted), and a boosted force is applied to a master cylinder. Thus, such a device assists an operator of the vehicle when braking. Typically, the device is utilized with a mechanically driven vehicle. Thus, in order to apply the brake, the operator will typically have taken a foot off an accelerator pedal to apply it to a brake pedal, or alternatively will simultaneously depress a clutch pedal with one foot and the brake pedal with another foot. In either event, the driving input to the vehicle wheels ceases via a mechanism other than the combined brake master cylinder and booster. In other words, the combined brake master cylinder and booster plays no part in the ceasing of the driving input to the vehicle wheels.

SUMMARY OF THE INVENTION

The present invention provides a combined master cylinder and dump valve including a body having a body bore, a brake port, a tank port, and a pressure port. The brake port, the tank port, and the pressure port are each hydraulically connected with the body bore. A piston is slidable within the body bore.

The piston delimits a part of the body bore to define a master cylinder for pressurizing the brake port. The piston includes a piston seal for isolating the pressure port from the tank port. The piston also includes a piston bore, a first piston hole set for hydraulically connecting the pressure port to the piston bore, and a second piston hole set for hydraulically connecting the piston bore to the tank port. A plunger is slideably received in the piston bore. A plunger hole set selectively connects the first piston hole set with a plunger bore, and a plunger seal arrangement selectively isolates the first piston hole set from the plunger bore.

The plunger bore is hydraulically connected to the piston bore such that, in a rest condition, the master cylinder is unpressurized and the plunger seal arrangement isolates the first piston hole set from the plunger bore, thereby isolating the pressure port from the tank port. In an actuated condition, the plunger acts to slideably move the piston to pressurize the brake port, and the plunger hole set hydraulically connects the first piston hole set with the plunger bore, thereby hydraulically connecting the pressure port to the tank port.

The present invention also provides a method of manufacturing one of a combined master cylinder and dump valve and a combined master cylinder and booster. The method includes the steps of providing a body suitable for manufacturing either a combined master cylinder and dump valve or a combined master cylinder and booster, providing a first set of components for assembling with the body to provide a combined master cylinder and dump valve, providing a second set of components for assembling with the body to provide a combined master cylinder and booster. The method also includes the step of assembling one of the first set of components or the second set of components with the body to provide one of a combined master cylinder and dump valve or a combined master cylinder and booster.

The present invention also provides a method of manufacturing a combined master cylinder and dump valve and a combined master cylinder and booster including the steps of providing two identical bare body castings, machining a first bare body casting in a first manner to provide a combined master cylinder and dump valve body, and machining a second bare body casting in a second different manner to provide a combined master cylinder and booster body. The method also includes the steps of assembling a first set of components with the combined master cylinder and dump valve body to provide a combined master cylinder and dump valve and assembling a second set of components with the combined master cylinder and booster body to provide a combined master cylinder and booster.

A significant number of components of a known combined master cylinder and booster valves can be utilized to provide a combined master cylinder and dump valve. This potentially reduces both the cost of the known combined master cylinder and booster valves and the cost of a new combined master cylinder and dump valves.

These and other features of the present invention will be best understood from the following specification and drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 4show a vehicle1including an engine2drivingly coupled to a hydraulic pump3. A hydraulic line4couples an output from the hydraulic pump3to an input of a hydraulic motor5. The hydraulic motor5is drivingly coupled to wheels6of the vehicle1. The output from the hydraulic motor5returns to a hydraulic tank7via a hydraulic line8. Extending from the hydraulic line4is a hydraulic line9, which is connected to a pressure port10of a combined master cylinder and dump valve11according to the present invention. A hydraulic line12connects a tank port13of the combined master cylinder and dump valve11to the hydraulic tank7. A hydraulic line15connects a brake port14of the combined master cylinder and dump valve11to a brake16. Operation of the vehicle is as follows.

To drive the vehicle, the engine2drives the hydraulic pump3, which takes hydraulic fluid from the hydraulic tank7and pressurizes it. The pressurized fluid is then fed along the hydraulic line4to the hydraulic motor5, which rotates and, in turn, rotates the wheel6and hence moves the vehicle1. When a vehicle operator needs to brake the vehicle1, the vehicle operator will apply a foot to the foot brake pedal, and dump valve components of the combined master cylinder and dump valve11will vent the hydraulic line4to the hydraulic tank7via the hydraulic line9and the hydraulic line12. Master cylinder components of the combined master cylinder and dump valve11then hydraulically pressurize the hydraulic line15, thereby applying the brakes16.

The combined master cylinder and dump valve11can be seen in more detail inFIG. 2. The combined master cylinder and dump valve11includes a body20, which is typically formed as a casting and then subsequently machined. The body20includes a central body bore22having a first cylindrical portion24of a diameter d and a second cylindrical portion26of diameter D. The pressure port10and the tank port13are both hydraulically connected to the second cylindrical portion26, and the brake port14is hydraulically connected to the first cylindrical portion24.

The first cylindrical portion24defines a master cylinder24A, and the second cylindrical portion26defines a body main cylinder26A. A master cylinder recuperation hole28is capable of selectively hydraulically connecting the master cylinder24A with the body main cylinder26A.

A piston30is slideably mounted within the body20. A first end32of the piston30is received within the first cylindrical portion24, and the remainder of the piston30is generally received within the second cylindrical portion26. The first end32includes a master cylinder seal34.

A first piston land36receives a first piston seal37for sealing the first piston land36to the second cylindrical portion26. A second piston land38receives a second piston seal39for sealing the second piston land38to the second cylindrical portion26. The first piston land36and the second piston land38are spaced apart axially and define an annular region40of the body main cylinder26A. The piston30includes a piston bore42and a first piston hole set44which includes a series of circumferentially spaced radially orientated holes (only two of which are shown) that hydraulically connect the annular region40with the piston bore42.

The piston30, and in particular the first piston land36, together with the body main cylinder26A define an annular region46to the left of the first piston land36when viewingFIG. 2. A second piston hole set48includes a series of radially orientated holes (only two are shown) that hydraulically connect the piston bore42with the annular region46. A check valve50is capable of selectively allowing the hydraulic fluid to flow from the piston bore42into the master cylinder24A.

The piston bore42includes a cylindrical portion43having a diameter E. A first end52A of a plunger52is slideably mounted within the cylindrical portion43(of diameter E). A plunger seal arrangement54including a first plunger seal55and a second plunger seal56, both in sealing relationship with the walls of cylindrical portion43, is mounted in the first end52A. The first plunger seal55is axially spaced from the second plunger seal56.

The first end52A of the plunger52further includes a plunger hole set58which hydraulically connects a region of the piston bore42to the right (when viewingFIG. 2) of the second plunger seal56with a plunger bore60of the plunger52.

A circlip62is mounted in a groove of the piston30and retains the plunger52generally within the piston bore42. A second end52B of the plunger52includes a groove64that receives a third plunger seal65. The second end52B further includes a recess66which receives a push rod67.

A closing spigot68has a generally top hat cross section and includes a land having a spigot seal69to seal between the land and the second cylindrical portion26. The closing spigot68includes a central bore70having a diameter F for slideably receiving the second end52B of the plunger52, and in particular for sealingly engaging the third plunger seal65. In use, the closing spigot68does not move relative to the body20. The spigot seal69prevents the leakage of hydraulic fluid outside of the combined master cylinder and dump valve11. A closing plate72is secured to the body20via a bolt (not shown) or studs and nuts (not shown) which engage threaded holes74.

A first resilient means in the form of a first spring76acts between a first spring abutment77of the piston30and a spring abutment78of the plunger52to bias the first spring abutment77and the spring abutment78apart. A second resilient means in the form of a second spring80acts between a spring abutment81of the body20and a second spring abutment82(in this case the first piston land36) of the piston30to bias the spring abutment81and the second spring abutment82apart.

The plunger52includes a plunger abutment84, and the piston30includes a corresponding piston abutment86. In the rest condition as shown inFIG. 2, the plunger abutment84and the piston abutment86are spaced apart by a distance x. Operation of the combined master cylinder and dump valve11is as follows.

An operator pedal force is applied to the push rod67which initially moves the plunger52to the left relative to the piston30, thereby progressively closing the distance x between the plunger abutment84and the piston abutment86and hydraulically connecting the pressure port10with the tank port13, thereby operating as a dump valve. When the plunger abutment84contacts the piston abutment86, the piston30moves to the left such that master cylinder seal34moves past the recuperation hole28, thereby sealing the master cylinder24A and allowing the brake port14to be pressurized to apply the brakes16.

FIG. 4shows a detailed schematic view of the combined master cylinder and dump valve11with the body20being represented by the chain dotted line. The three ports (the pressure port10, the tank port13and the brake port14) connect the associated external hydraulic lines with the body20. It is important that no air enters the master cylinder24A, and thus the check valve50and the master cylinder recuperation hole28must recuperate the master cylinder24A from a region of the body20that is full of hydraulic fluid. In this case, the recuperation hole28and the check valve50both recuperate the master cylinder24A from the annular region46, which effectively acts as an internal tank. This internal “tank” is illustrated inFIG. 4.

The pressure port10is permanently hydraulically connected to the annular region40because the first piston seal37is always located to the left of the pressure port10when viewingFIG. 2, and the second piston seal39is always located to the right of the pressure port10even at the extreme of movement of the piston30towards the left when viewingFIG. 2. The annular region40is in permanent hydraulic connection with the first piston hole set44. The tank port13, the annular region46, the second piston hole set48, the piston bore42, the plunger bore60and the plunger hole set58are all permanently hydraulically connected to each other. The hydraulic connection between the master cylinder24A and the annular region46is selectively blocked as the master cylinder seal34passes to the left of the recuperation hole28.

As shown inFIG. 2, the plunger seal arrangement54ensures that the first piston hole set44is hydraulically isolated from the plunger hole set58(and hence isolates the first piston hole set44from the second piston hole set48). However, as the second plunger seal56moves to the left of the first piston hole set44, the first piston hole set44becomes hydraulically connected with the plunger hole set58(and hence hydraulically connects the first piston hole set44with the plunger bore60). The check valve50selectively allows for recuperation of the master cylinder24A in a known manner.

FIG. 2shows the combined master cylinder and dump valve11in a rest position with no force being applied to the push rod67. The second spring80acts to bias the piston30into abutting engagement with the closing spigot68, which acts as a stop. Similarly, the first spring76biases the plunger52to the right when viewingFIG. 2and into abutting engagement with the circlip62. In this position, the recuperating holes28are open, and the first piston hole set44has been closed by the plunger seal arrangement54. The pressure port10cannot vent to the tank port13, and hence the hydraulic line9is closed. Thus, the hydraulic pump3is capable of driving the hydraulic motor5.

Preferably, the pressure port10is hydraulically connected to the tank port13(i.e., the dump valve is opened) before the master cylinder24A pressurizes the brake port14(i.e., prior to the brakes being applied). To achieve this function, the first spring76, the second spring80and the distance x between the plunger abutment84and the piston abutment86must be correctly designed. By way of example, one installation may have an installed pre-load on the second spring80of 200 Newtons. The first spring76may have an installed pre-load of 60 Newtons, and the distance x may be 7 mm. The spring rate of the first spring76would be 140 Newtons per 7 mm.

The installed pre-load of the first spring76, when the combined master cylinder and dump valve11is in the rest position, is less than the installed pre-load of the second spring80. Thus, when a force is applied to the push rod67, the first spring76will compress before the second spring80. As the push rod67moves to the left, the piston30initially remains stationary, and the plunger seal arrangement54moves to the left relative to the stationary first piston hole set44. Further movement of the push rod67to the left causes the distance x between the plunger abutment84and the piston abutment86to further close. The second plunger seal56ultimately will move to the left of the first piston hole set44, thereby hydraulically connecting the pressure port10to the tank port13and hence opening the dump valve.

As the plunger abutment84and the piston abutment86contact each other, the first spring76compresses by 7 mm and therefore exerts a load of 200 Newtons (i.e., an initial installed load of 60 Newtons plus 7 mm of compression at a rate of 140 Newtons per 7 mm compression). As the plunger abutment84and the piston abutment86contact each other, the spring load exerted by the first spring76is substantially equal to the spring load exherted by the second spring80. Further movement of the push rod67to the left causes the plunger abutment84to press on the piston abutment86, thereby moving the piston30to the left, closing the recuperation hole28, and pressurizing the master cylinder and the brake port14.

The release of the brake pedal causes the components to return the position shown inFIG. 2, thereby releasing the brake16and closing the dump valve and allowing the hydraulic pump3to drive the hydraulic motor5to move the vehicle.

As shown inFIG. 2, the first piston hole set44includes a plurality of holes spaced circumferentially around the piston30. All the holes are formed at the same longitudinal position of the piston30.

In a further preferred embodiment, the first piston hole set44can include a series (e.g., at least two or at least three) of spaced holes, preferably circumferentially spaced, with each hole being at a different longitudinal position of the piston30. Clearly, if the plunger seal arrangement is in the form of a first plunger seal and a second plunger seal, then the first and second plunger seals must be spaced apart sufficiently to encompass all the holes of the first piston hole set44to ensure that the first piston hole set44is hydraulically isolated from the first plunger hole set58and a central region of the piston bore42. In a preferred embodiment, the holes of the first piston hole set44are formed as part of a helix around the piston30circumference.

In one example, the first piston hole set44may include sixteen radially orientated holes each having a diameter of 1.5 mm. When formed as a helix, adjacent holes can be longitudinally offset by 0.2 mm. Thus, the actual distance between the first hole and the sixteenth hole would be 3 mm (i.e., 15 gaps×0.2 mm=3 mm). Furthermore, the total distance travelled by the plunger52, relative to the piston30, between when the first piston hole is starting to open and when the last piston hole is fully open is 4.5 mm (i.e., fifteen gaps×0.2 mm+1 hole diameter (1.5 mm)=4.5 mm). By arranging the holes in this manner, it is possible to provide a dump valve that progressively opens. This is particularly beneficial since it allows the operator to “inch forward” the vehicle1in a controlled manner, thereby allowing for good control of the vehicle1at very slow speeds. The term “hole set” covers a set having any number of holes, including just a single hole.

As mentioned above, the holes are preferably provided on a helix, though it is not necessary to provide the holes in this form in order to provide a first piston hole set44wherein different holes are positioned at different longitudinal positions on the piston30.

Typically, the sixteen hole arrangements mentioned above might be used in conjunction with a distance x between the plunger abutment84and the piston abutment86of 7 mm. This allows for manufacturing tolerance errors and an initial movement of the plunger52(for example 2 mm) between the rest position and a position where the first of the sixteen holes starts to open.

The spring force of the first spring76, when compressed by the distance x (200 Newtons), is substantially equal to the spring force of the second spring80when in a rest condition (also 200 Newtons). This provides for a good pedal feel and a substantially seamless transition from the dump valve being fully open to the start of the brakes being applied.

Certain components of the combined master cylinder and dump valve11act as a master cylinder, and certain other components of the combined master cylinder and dump valve11act as a dump valve (shown generally by the arrow90). The dump valve90and the master cylinder act sequentially, i.e. the dump valve90opens, and then the master cylinder applies the brakes.

FIG. 2shows various elastomeric seals. Under certain circumstances, where a limited amount of seal leakage can be tolerated, certain seals can be defined by a simple piston land or a plunger land in the absence of any elastomeric or other separate “sealing” component.

The present invention adapts a known combined master cylinder and booster to provide a combined master cylinder and dump valve11.FIG. 3shows a known combined master cylinder and booster110. Certain components of the combined master cylinder and booster110are identical to the components of the combined master cylinder and dump valve11. In particular, the body20, the master cylinder seal34, the check valve50, the first piston seal37, the second piston seal39, the third plunger seal65, the first plunger seal55, the second plunger seal56, the closing plate72, the closing spigot68, the closing spigot seal69, and the push rod67are identical.

These components may look different simply becauseFIG. 3is an engineering manufacturing drawing, andFIG. 2is a schematic drawing. By way of explanation,FIG. 3includes protective caps over the ports which are removed prior to fitting the valve.

When a combined master cylinder and dump valve11according to the present invention is manufactured by adapting a known combined master cylinder and booster110, the combined master cylinder and dump valve11may have a body bore which includes a body main cylinder engaged by a piston seal. The body main cylinder has a diameter (D). A plunger152includes a seal in slideable engagement with a spigot wall, and the spigot wall is fixed relative to the body main cylinder and has a spigot wall diameter (F). The body main cylinder (D) is at least 1.412 times larger than the spigot wall diameter (F), alternatively at least 1.732 times larger, alternatively at least 2.000 times larger, or alternatively at least 2.236 times larger.

Operation of combined master cylinder and booster110is known, but will now be briefly described. A first piston hole set144of a piston130includes a series of circumferentially spaced, radially orientated holes. However, all the holes are located at the same axial position on the piston. A second piston hole set148also includes a series of circumferentially spaced radially orientated holes that are all located at the same longitudinal position on the piston130. The first piston hole set144is positioned just to the left of the second plunger seal56, and the second piston hole set148is positioned just to the left of the first plunger seal55.

As the push rod67moves to the left by operating a foot brake, the plunger52initially moves to the left such that the first plunger seal55and the second plunger seal56initially close all of the holes of their corresponding piston hole sets148and144. Continued movement of the push rod67to the left causes the first plunger seal55and the second plunger seal56to partially open all of the holes of their corresponding hole set148and144. This allows pressurized fluid from the pressure port10to enter the plunger bore160, causing the piston130to move to the left and resulting in the first plunger seal55and the second plunger seal56closing all of their corresponding holes. This pressurized fluid then becomes trapped in the plunger bore160and acts on the plunger152(the effective working diameter of the plunger152is equivalent to the diameter F of the spigot wall) to force the plunger152to the right when viewingFIG. 3and acts on the diameter D of the piston130to force the piston130to the left when viewingFIG. 3. Since the diameter D is larger than the diameter F, the force applied to the push rod67is “boosted” by the ratio of (D×D/F×F), and hence the force applied to a master cylinder piston portion131of the piston130is greater than the force applied to the push rod67.

To provide a boost ratio of 2-1, the diameter D of the piston130needs to be 1.412 times larger than the diameter F of the plunger52. Boost ratios of 3-1, 4-1 and 5-1 can be provided by ensuring that the diameter D is 1.732, 2.000, 2.236 times larger than the diameter F, respectively.

Both a first spring176and a second spring180are partially compressed when the booster is operating to boost a push road load. This can be contrasted with a combined master cylinder and dump valve11according to the present invention, wherein during progressive opening of the dump valve, the first spring76is compressed and the second spring80remains in the initially installed condition.

A comparison of the piston30and the piston130shows relatively few differences. The main difference is the position of the second piston hole sets48and148. In particular, the master cylinder piston portion131can be identical to the corresponding portion of the piston30.

Furthermore, a comparison of the plunger52and the plunger152again shows relatively few differences. The main difference is in the alternative positioning of the first plunger seal55. In particular, the second plunger seal56is located at the same position, and the part of the plunger152to the left of the second plunger seal56is identical to the corresponding part of the plunger52.

The present invention adapts a device (the combined master cylinder and booster110) having one type of valve (a booster valve) to a completely different device (combined master cylinder and dump valve11) having a completely different sort of valve (a dump valve) for use in a completely different application. This adaptation has been carried out using a considerable number of common components, potentially providing both a cheaper combined master cylinder and dump valve11and a combined master cylinder and booster110.

There is no “boosting” aspect to the combined master cylinder and dump valve11. The boost ratio of the combined master cylinder and booster110is dependent upon the relative diameters F and D. It is possible to retain the same diameters D and F of a combined master cylinder and booster110and apply them to a combined master cylinder and dump valve11, even though the relative diameters play no part in the operation of the combined master cylinder and dump valve11.

Typically, the body20will be made from a casting. Where there are minor differences between the finally machined body of a combined master cylinder and dump valve11and the finally machined body of a combined master cylinder and booster110(e.g., a different thread size on one or more of the ports), it is possible to use a common bare body casting and machine it in a slightly different manner to provide for the slightly differing combined master cylinder and dump valve11and combined master cylinder and booster110finally machined bodies. However, under other circumstances, it is possible to use the same bare casting and machine it in an identical manner (for example, the body20) to provide a body for both a combined master cylinder and dump valve11and a combined master cylinder and booster110.

Similarly, it is possible to provide a common bare piston casting which is machined in a slightly different manner to provide a combined master cylinder and dump valve piston or a combined master cylinder and booster piston. Similarly, the plunger may be provided as a common bare casting and machined slightly differently to provide a combined master cylinder and dump valve plunger or a combined master cylinder and booster plunger.

It is possible to produce identical bare castings and under certain circumstances, machine the bare castings in an identical manner to provide for devices (a combined master cylinder and dump valve11or a combined master cylinder and booster110) that have significantly different applications.