Hydraulic lash adjuster

1. A hydraulic lash adjuster for an engine valve train, the hydraulic lash adjuster comprising:

a hydraulic lash adjusting arrangement configured to automatically compensate for lash in the engine valve train, the hydraulic lash adjusting arrangement comprising:

a first chamber configured to contain hydraulic fluid;

a second chamber configured to contain hydraulic fluid, the second chamber being located above the first chamber;

a third chamber configured to contain hydraulic fluid, the third chamber being located above the second chamber;

a first body;

a second body disposed for sliding reciprocal movement within the first body;

a first valve between the first chamber and the second chamber, the first valve comprising a ball captured by a cage; and

a third body disposed for sliding reciprocal movement within the second body;

a lost motion arrangement configured to inhibit motion, induced in the engine valve train in response to a lift profile of a rotating cam, from being transferred to an engine valve, the lost motion arrangement comprising:

the second body; and

the third body; and

a relief valve configured to open an aperture into the second chamber, the relief valve extending along a central axis of the second chamber, the central axis extending axially through the aperture, the relief valve comprising an elongate stem or needle that extends along a longitudinal axis of the third chamber and through an upper wall of the hydraulic lash adjuster,

wherein the first, second and third bodies are configured so that a displacement of hydraulic fluid in the first chamber resulting from a relative movement between the second body with respect to the first body results in a pressure difference between the first chamber and the second chamber so as to move the third body, inhibiting motion induced in the engine valve train in response to the lift profile of the rotating cam from being transferred to the engine valve, and

wherein the first chamber comprises a space defined by the first body, the second body, and the third body.

2. The hydraulic lash adjuster of claim 1 , which can be configured in a first operational mode and a second operational mode,

wherein, in the first operational mode, the lost motion arrangement is enabled, and

wherein, in the second operational mode, the lost motion arrangement is disabled.

3. The hydraulic lash adjuster of claim 1 further comprising:

a stop member configured to stop further movement of the third body when the third body moves into contact with it,

wherein the hydraulic lash adjuster then acts as a solid body.

4. The hydraulic lash adjuster of claim 3 , further comprising:

a biasing element configured to bias the third body away from the stop member.

5. The hydraulic lash adjuster of claim 3 , wherein the stop member is integral with the second body.

6. The hydraulic lash adjuster of claim 3 , wherein the stop member is a component of the second body.

7. The hydraulic lash adjuster of claim 1 , wherein, in use, when the relief valve is open, the lost motion arrangement is enabled, and when the relief valve is closed hydraulic fluid in the first chamber and the second chamber causes the hydraulic lash adjuster to act as a solid body so as to disable the lost motion arrangement.

8. The hydraulic lash adjuster of claim 7 , wherein the aperture fluidly connects the second chamber and the third chamber when the relief valve is open.

9. The hydraulic lash adjuster of claim 7 , further comprising:

an actuator configured to actuate the relief valve.

10. The hydraulic lash adjuster of claim 1 , wherein the cage of the first valve is supported by the third body, and

wherein the first valve is carried by the third body when the third body moves.

11. The hydraulic lash adjuster of claim 1 , further comprising:

a first biasing element configured to bias the second body away from the first body.

12. The hydraulic lash adjuster of claim 11 , further comprising:

a second biasing element configured to bias the third body away from a stop member of the hydraulic lash adjuster, the stop member being configured to stop further movement of the third body when the third body moves into contact with it.

13. A valve train for an engine, comprising the hydraulic lash adjuster of claim 1 .

14. The valve train of claim 13 , wherein the lost motion arrangement is useable to inhibit an additional valve lift of the engine valve.

15. The valve train of claim 14 , wherein the engine valve is an exhaust valve.

16. The valve train of claim 15 , wherein the additional valve lift is a de-compression engine brake valve event which the lost motion arrangement inhibits when in an engine combustion mode.