IMPROVEMENTS RELATING TO ELECTRO-HYDRAULIC BRAKING SYSTEMS

Abstract: In an electro-hydraulic braking system a housing is provided having at least three discrete housing portions (1, 2, 3), a first portion being adapted to contain electrical drive circuitry for said at least one actuator, the second portion being adapted to contain hydraulic flow passages to and from the electrically operated actuator, and the third portion being adapted to house one or more pressure sensors. On assembly of the housing, electrical contacts from the one or more pressure sensors in the third portion provide a connection between the one or more pressure sensors and the electrical circuitry contained in the first portion, and hydraulic passages extending from the pressure sensors in the third portion provide a connection between one or more pressure sensors and fluid passages in the second portion.

Description: IMPROVEMENTS RELATING TO ELECTRO-HYDRAULIC BRAKING SYSTEMS This invention relates to electro-hydraulic braking systems of the kind in which at least one electrically operated actuator is provided in a brake line between a fluid source and a brake, operation of the electrically operated actuator selectively connecting and disconnecting the brake to the pressure source, and in which a pressure sensor is provided which is adapted to sense the fluid pressure in a part of the braking system. The provision of at least one pressure sensor in the hydraulic circuit enables a measure of circuit performance and behaviour to be made. Because the system comprises both electrical circuitry - for control of the actuators and interrogation of the pressure sensors - and hydraulic circuitry, there is a problem of leakage of fluid from the hydraulic circuit affecting the electrical circuit. In the past, it has been known to incorporate the hydraulic and electrical components into a two part housing. One part of the housing contains the electrical circuitry for controlling the actuators. The other part contains the hydraulic passages for the brake fluid. Where the electrically operated actuators are controlled by a solenoid which comprises of an armature working with a coil, the coils of the solenoid are adapted to be fixed relative to and extend from the first housing. The armature is then adapted to extend from the second housing and be sealed therewith. As the two halves of the housing are placed together, the coils pass over the armature to complete the magnetic circuit of the electrically - controlled actuators. In accordance with the present invention, in an electro-hydraulic braking system of the kind set forth a housing is provided having at least three discrete housing portions, a first portion being adapted to contain electrical drive circuitry for said at least one actuator, the second portion being adapted to contain hydraulic flow passages to and from the electrically operated actuator, and the third portion being adapted to house one or more pressure sensors, in which on assembly of the housing, electrical contacts from the one or more pressure sensors in the third portion provide a connection between the one or more pressure sensors and the electrical circuitry contained in the first portion, and hydraulic passages extending from the pressure sensors in the third portion provide a connection between the one or more pressure sensors and fluid passages in the second portion. Thus, the invention provides a separate housing portion for one or more pressure sensors. This allows the pressure sensor (s) to be easily replaced or removed from both the electrical circuitry and the hydraulic circuits. Preferably, the third portion comprises a body having one or more through bores, a pressure sensor being provided within a respective bore. Each sensor may be provided within a tube which is adapted to fit within a bore in the body, an end portion of the tube extending outwardly away from the bore. The end portion of tube can be inserted into a corresponding recessed hole in the second portion to provide a hydraulic connection. Electrical connections to the pressure sensor may extend from one end of the tube. As an alternative the main body may be split into two halves which clamp around the tube or tubes containing the pressure sensors. Of course, the tubes could be omitted in at least one alternative. A temperature sensor may be provided within the pressure sensor housing to allow the temperature of the hydraulic fluid to be measured. A temperature sensor may be provided for each pressure sensor, to measure the temperature of the fluid reaching each pressure sensor. Alternatively, any number of temperature sensors may be provided. The third portion housing the pressure sensors may further include an engagement means adapted to enable the pressure sensor housing to be mechanically secured to the first housing portion. The engagement means may comprise a number of holes adapted to receive one or more bolts which engage with threaded blind bores in the first housing portion. Alternatively, the pressure sensor housing may be a snap-fit engagement with the first housing portion. The openings in the ends of the tubes which allow fluid from the second housing to reach the pressure sensors may extend axially in the same direction as the axis of the coils for the solenoid valves, so that the pressure sensor tubes readily slide into the respective holes in the second portion simultaneous with the coils sliding around and onto the armatures of the flow valves during assembly. An annular seal such as an elastomeric seal may be provided around the end of each protruding portion of tube to form a fluid tight seal within the respective hole in the second portion on assembly. The seal may be located in a groove extending around the tube. A second annular seal may be provided between the tube and the bore in the third portion. Alternatively, or additionally, an elastomeric seal may be provided in a recess which links the ends of all the tubes. The seal may be located in a recess in a face of the third body. The individual seals could then be omitted from each tube. In yet another alternative, the recess linking the ends of the tubes may be adapted to connect a portion of the end of the tube to atmosphere when the third portion is pressed against the second portion to ensure there is no difference between the pressure on the side of the second housing and the measured pressure on the side of the third housing. The electrical circuitry may be sealed within the first portion at least with respect to the interface between the first portion and the second portion. One or more solenoid coils may be located in or mounted on the first portion, each coil forming a part of a solenoid for a respective electrically controlled valve. The armature corresponding to each valve may be supported by the second portion. The armature may be sealed to prevent leakage of fluid past the armature/housing interface. The armature may pass into the coil when the first and second housing portions are assembled together. The third portion may be adapted to be received, at least partially, within a recess in the first portion. When the first and second portions are assembled, the third portion may be completely encased by the first and second portions. The first and second housing portions may be provided with a continuous seal around a perimeter of the mating faces to seal the inside of the two housing portions together when assembled. There will now be described, by way of example only, one embodiment of the present invention with reference to the accompanying drawings of which. Figure 1 is a perspective view of a first housing portion of a three-part housing for part of an electro-hydraulic braking system; Figure 2 is a perspective view of a second housing portion of the three-part housing of figure 1 ; Figure 3 (a) is a first perspective view and (b) is a second perspective view of a third housing portion of the three-part housing; and Figure 4 shows the fully assembled three-part housing portions. Figures 1 to 3 illustrate three portions 1 ,2,3 of a three-part housing for part of an electro-hydraulic braking system. The system comprises a number of solenoid actuated flow control valves. Each of the valves include a solenoid comprising an electrical coil 4 which surrounds an armature 5 when assembled. An electrical drive circuit contained within the first portion supplies current to one or more of the coils 4 in response to a braking demand signal to move the armature 5, in turn to open and close the valves. In order to provide isolation between the hydraulic part of the circuitry and the electrical part of the circuit, the valves are split into two parts. A first part comprising of the coils 4 is mounted relative to the first housing portion 1 which contains the electrical drive circuitry. A second part comprising of the armature 5 of the hydraulic valve and the hydraulic fluid lines are provided in the second housing portion 2 with the armature 5 protruding from a mating face of the second portion 2. On assembly of the housing, the first and second housing portions are pushed together so that each armature slides into the respective coil. This completes the valve assembly. Such an arrangement is beneficial in allowing the electrical circuitry to be easily removed from the hydraulic circuitry without any need for draining the hydraulic fluid since no hydraulic connections are altered. In addition to housing the electric drive circuitry and the solenoid coils the first housing portion includes a recess in the mating face adapted to receive the third housing portion 3 shown in figures 3 (a) and 3 (b) of the accompanying drawings. The third portion comprises of a main body which receives a number of pressure sensors (not shown). Each pressure sensor is provided at the end of a tube 6 adapted to be inserted in a bore on the main body. The tubes receive hydraulic fluid from passages 10 in the second housing portion 2. Electrical connectors 8 extend from the rear of the pressure sensors to allow electrical connections between the pressure sensors and further electrical circuitry in the first housing 1. Each tube associated with a respective pressure sensor is provided with a circumferential elastomeric seal 11. The seal 11 forms a fluid tight seal between the tube and the bore in the housing. Each tube extends beyond the housing and carries a second circumferential seal 9 adjacent its extended end. The extended portion of tube is adapted to fit within the passage 10 in the second housing portion 2 which connects to a part of the hydraulic circuit. As shown in the accompanying figures, the main body carries seven sensors in a line. The axis of the tubes for the sensors is selected to coincide with the axis of the solenoid coils so that the tubes enter the respective holes in the second housing as the coils are slid over the armatures. A recess 20 connects the ends of the tubes 6 so that as the seals on the end of the holes 6 are pressed into the openings in the second housing portion, atmospheric pressure is present on the side of the seals on the end of the tubes which faces away from the second housing. The recess 20 may therefore be connected by an extending passage 21 to the atmosphere. Alternatively, it may receive an elastomeric seal (not shown) . As shown in figure 2, the second housing 2 also carries a casing for an electric motor or pump and a pressure accumulator 13. Of course, the electric motor 12 could be mounted onto the first housing portion. Finally, as shown in figure 2, a number of connecting ports 14 allow brake lines to be connected to the hydraulic circuitry in the second housing to connect fluid supply and brakes to the solenoid-actuated valves.

Claims: CLAIMS 1. An electro-hydraulic braking system in which at least one electrically operated actuator (4,5) is provided in a brake line between a pressure source of hydraulic fluid and a brake, operation of the electrically operated actuator (4,5) selectively connecting and disconnecting the brake to the pressure source, and in which at least one pressure sensor is adapted to sense fluid pressure in a part of the braking system, the system being characterised by a housing (1 ,2,3) having at least three discrete housing portions, a first portion (1) being adapted to contain electrical drive circuitry for the actuator, a second portion (2) being adapted to contain hydraulic flow passages to and from the electrically operated actuator, and a third portion (3) being adapted to house the pressure sensor, in which on assembly of the housing (1,2,3) electrical contacts (8) from the pressure sensor in the third portion (3) provide a connection between the pressure sensor and the electrical drive circuitry contained in the first portion, and hydraulic fluid passages (10) extending from the pressure sensor in the third portion (3) provide a connection between the pressure sensor and fluid passages (10) in the second portion (2) . 2. An electro-hydraulic braking system according to claim 1 characterised in that the third portion (3) comprises a body having at least one through bore, a pressure sensor being provided within the bore. 3. An electro-hydraulic braking system according to claim 2 characterised in that each sensor is provided within a tube (6) which is adapted to fit within a respective bore in the body, an end portion of the tube (6) extending outwardly away from the bore. 4. An electro-hydraulic braking system according to claim 2 characterised in that the body is split into two halves which clamp around the tube or tubes containing the pressure sensors. 5. An electro-hydraulic braking system according to any preceding claim, characterised in that at least one temperature sensor is provided within the pressure sensor housing to allow the temperature of the hydraulic fluid to be measured. 6. An electro-hydraulic braking system according to claim 5 characterised in that a temperature sensor is provided for each pressure sensor, to measure the temperature of the fluid reaching each pressure sensor. 7. An electro-hydraulic braking system according to any preceding claim, characterised in that the third portion housing the pressure sensors further includes an engagement means adapted to enable the pressure sensor housing to be mechanically secured to the first housing portion. 8. An electro-hydraulic braking system according to claim 7, characterised in that the pressure sensor housing is a snap-fit engagement with the first housing portion. 9. An electro-hydraulic braking system according to claim 3, characterised in that an annular seal is provided around the end of each protruding portion of tube to form a fluid tight seal within a respective bore provided in the second portion . 10. An electro-hydraulic braking system according to any preceding claim characterised in that one or more solenoid coils are located in or mounted on the first portion, each coil forming a part of a solenoid for a respective electrically controlled valve, an armature corresponding to each valve being supported by the second portion so that the armature passes into the coil when the first and second housing portions are assembled together.

Inventors: ANDERSON ROBERT ALAN, ANDERSON, ROBERT, ALAN
Applicants: ANDERSON ROBERT ALAN, LUCAS IND PLC, ANDERSON, ROBERT, ALAN, LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1999
Main classification: B60T8
IPC codes: B60T8, B60T15