Braking grid cooling system

1. A braking grid cooling system, the system comprising:

a fan having a hub supporting a rotor and at least partially enclosing a stator, and a plurality of fan blades connected to and projecting radially from the hub at an end thereof;

a dynamic braking grid having a radially outer wall, a radially inner wall adjacent the hub, the radially inner wall defining a central opening in the form of a passage that extends entirely through the dynamic braking grid, and a plurality of resistor elements extending between the radially outer wall and the radially inner wall, the passage receiving the fan hub in a nested relation to the dynamic braking grid such that a combined height of the dynamic braking grid and the fan is less than a sum of a height of the grid and a height of the fan; and

the fan blades positioned upstream and outside of the passage and aligned in an upstream direction with a space between the outer wall and the inner wall such that the fan blades move air in a longitudinal direction relative to the fan and in a linear flow through the dynamic braking grid and across the resistor elements to thereby cool the dynamic braking grid as it heats up when it receives electric current from a power source to power the fan.

2. The system of claim 1 , wherein the fan blades are aligned so that air is moved by the fan blades across the entire distance between the radially outer wall and the radially inner wall.

3. The system of claim 2 , wherein the dynamic braking grid is cylindrical in shape, and the fan is concentric with the grid.

4. The system of claim 3 , wherein the central opening is a passage that extends through the dynamic braking grid.

5. The system of claim 4 , wherein the grid includes an insulator electrically isolating the resistor elements from the outer wall and the inner wall.

6. The system of claim 5 , wherein the fan includes a support ring, and the support ring is attached to the grid outer wall.

7. The system of claim 6 , wherein the support ring is shaped to be mounted on a bulkhead, and wherein the support ring supports the fan and braking grid.

8. The system of claim 6 , wherein the fan includes a stator housing and a plurality of support struts extending between the stator housing and the support ring.

9. The system of claim 8 , wherein the fan includes a plurality of turning vanes attached to the support struts.

10. The system of claim 9 , wherein the fan includes an inner vane support ring attached to the support struts and an outer vane support ring attached to the support struts; and wherein the vanes are attached to and extend between the inner vane support ring and the outer vane support ring.

11. The system of claim 10 , wherein the stator housing includes a cylindrical body and a mounting ring attached to the body; and wherein the support struts are attached to the mounting ring.

12. The system of claim 11 , wherein stator includes a top flange and a bottom flange; and the stator includes an end plate attached to the end flange.

13. The system of claim 12 , wherein the rotor includes a central shaft rotatably mounted on the top flange and end plate; and wherein the hub is attached to the central shaft.

14. The system of claim 1 , wherein the hub is nested in the passage to not extend above an upper surface of the braking grid.

15. A diesel-electric vehicle having a roof panel, the vehicle comprising:

a braking grid cooling system mounted in the roof panel the system including a fan having a motor with a stator, a dome-shaped hub, a rotor mounted on the hub, and a plurality of fan blades connected to and projecting radially from the hub at an end thereof:

a dynamic braking grid extending below the roof panel the dynamic braking grid having a radially outer wall, a radially inner wall adjacent the hub, the radially inner wall defining a central opening in the form of a passage that extends entirely through the dynamic braking grid, and a plurality of resistor elements extending between the radially outer wall and the radially inner wall, the passage opening receiving the fan hub in a nested relation to the dynamic braking grid such that a combined height of the dynamic braking grid and the fan is less than a sum of a height of the grid and a height of the fan; and

the fan blades positioned upstream and outside of the passage and aligned in an upstream direction with a space between the outer wall and the inner wall such that the fan blades move air in a longitudinal direction relative to through the fan and in a linear flow through the dynamic braking grid and across the resistor elements to thereby cool the dynamic braking grid as it heats up when it receives electric current from a power source to power the fan.

16. The vehicle of claim 15 , wherein the fan blades are positioned immediately upstream of the braking grid such that rotation of the hub causes air to pass through the grid in an axial direction of the fan and in an axial direction of the dynamic braking grid.

17. The vehicle of claim 16 , wherein the fan includes a support ring and a plurality of turning vanes extending between the motor and the support ring immediately upstream of the fan blades.

18. The vehicle of claim 17 , wherein the support ring is attached to and supports the dynamic braking grid.

19. The vehicle of claim 17 , wherein the fan includes a plurality of support struts connecting the motor to the support ring, and the turning vanes are attached to and supported by the support struts.

20. The vehicle of claim 5 , wherein the vehicle is selected from a diesel-electric locomotive traction engine, and a diesel-electric off-highway mining truck.

21. A method of cooling a dynamic braking grid, the braking grid having a radially outer wall, a radially inner wall defining a central opening in the form of a passage that extends entirely through the dynamic braking grid, and a plurality of resistor elements extending between the radially outer wall and the radially inner wall connected to power the fan, the method comprising:

providing a fan having a hub supporting a rotor and at least partially enclosing a stator, and a plurality of fan blades connected to and projecting radially from the hub at an end thereof: positioning the fan in a nested relation to the dynamic braking grid such that a combined height of the dynamic braking grid and the fan is less than a sum of a height of the grid and a height of the fan, and the fan blades are positioned upstream and outside of the passage and aligned in an upstream direction with a space between the outer wall and the inner wall such that the fan blades move air in a longitudinal direction through the fan and in a linear flow through the dynamic braking grid and across the resistor elements to thereby cool the dynamic braking grid as it heats up when it receives electric current from a power source to power the fan; and

actuating the fan to rotate the hub such that the fan blades move air through the braking grid in a linear direction parallel to an axis of the fan and an axis of the dynamic braking grid, and upwardly through the dynamic braking grid.