Class 700 tread brakes

[Bletchleyite]

Noticed today that 700s appear to have tread brakes on some axles.

Why is this? I thought they were considered outmoded these days.

 

[Domh245]

Noticed today that 700s appear to have tread brakes on some axles.

Why is this? I thought they were considered outmoded these days.

They have tread brakes on motored axles. The design of the bogie is to have inboard disk brakes, but this can't be done on the motored axles, where you have a gearbox somewhat in the way - so these are instead tread braked.

Unmotored Bogie

Motored Bogie

They also talk about how there is a reduction in unsprung mass, moment of inertia of the axle, and several other advantages in this presentation

Not sure why they went with this particular bogie architecture though, Bombardier have achieved comparable weights with their Flexx Eco bogie (which ISTR Phillip Phlopp saying is an evolution of an experimental BREL bogie) whilst retaining Disk Brakes. I haven't seen anywhere that sets out the rationale for this layout over the more conventional layout which has brake disks inset into the wheel, but it would seemingly be of marginal improvement otherwise other manufacturers would follow suit.

 

[TRAX]

Some trains have the disc brake directly integrated to the wheel - they could've done that if space was an issue, certainly more efficient than tread brakes...

 

[hwl]

They have tread brakes on motored axles. The design of the bogie is to have inboard disk brakes, but this can't be done on the motored axles, where you have a gearbox somewhat in the way - so these are instead tread braked.

Unmotored Bogie

Motored Bogie

They also talk about how there is a reduction in unsprung mass, moment of inertia of the axle, and several other advantages in this presentation


Not sure why they went with this particular bogie architecture though, Bombardier have achieved comparable weights with their Flexx Eco bogie (which ISTR Phillip Phlopp saying is an evolution of an experimental BREL bogie) whilst retaining Disk Brakes. I haven't seen anywhere that sets out the rationale for this layout over the more conventional layout which has brake disks inset into the wheel, but it would seemingly be of marginal improvement otherwise other manufacturers would follow suit.

Bombardier have the useful patents for that! hence everyone else has to do something different.
Hitachi is using traditional outside frame bogies for the motor bogies on the 385s and inside frame for the unpowered.
The Ecoflex model numbers are even a nod to their BR heritage: 50xx

The Aventra have a new "shorter" traction motor design to help things fit as well.

 

[100andthirty]

Modern dynamic brakes are so efficient that the work that has to be done by the tread brakes is small, hence, in this application, any disbenefits of tread brakes are not worth worrying about. Of course, the tread brakes have to do all the work to brake the motor cars in the event of an emergency brake application or if the traction package on one car fails. Modern three phase traction packages are very reliable.

 

[Bletchleyite]

Modern dynamic brakes are so efficient that the work that has to be done by the tread brakes is small, hence, in this application, any disbenefits of tread brakes are not worth worrying about. Of course, the tread brakes have to do all the work to brake the motor cars in the event of an emergency brake application or if the traction package on one car fails. Modern three phase traction packages are very reliable.

Is it worth using them more, then, e.g. to scrub the leaf mulch off the wheels?

 

[Domh245]

Is it worth using them more, then, e.g. to scrub the leaf mulch off the wheels?

As far as I can tell, the 345s (and presumably future Aventras) have got tread brakes on the leading axles, presumably for this exact reason. I can't think of any other reason why they'd have it this way.