Toyota’s K313: Examining hydraulic system - Transmission Digest

Toyota’s K313: Examining hydraulic system

We left off last month having already pulled the valve body from this little Toyota CVT unit. Once the valve body is removed, the 2-wire Hall-Effect turbine-shaft speed sensor (NT) can be seen bolted to the case where it reads the rotation of the forward clutch drum assembly.

Technically Speaking

  • Author: Wayne Colonna, Technical Editor
  • Subject Matter: Toyota K313 CVT
  • Issue: Valve body

Secondary pressure regulator valve regulates converter & lube pressure

Second in a series

We left off last month having already pulled the valve body from this little Toyota CVT unit. Once the valve body is removed, the 2-wire Hall-Effect turbine-shaft speed sensor (NT) can be seen bolted to the case where it reads the rotation of the forward clutch drum assembly.

Now that the valve body has been removed, the converter housing can be unbolted from the main case (Figure 1). Once the bolts and the housing are removed, the powerflow design quickly becomes evident. Like many other CVTs on the road, the secondary pulley drive gear meshes with the transfer gear, which drives the differential (Figure 2). Once these are removed, the pump can be unbolted (Figure 3) and removed from the transmission (Figure 4).

It looks like a typical pump but it does have an interesting design to it. When you separate the cover from the body to look at the gears, you see that it utilizes trochoidal gears making for a gerotor-style pump that is a positive displacement pump (Figure 5). These style gears have been around for quite some time in various transmissions making it a familiar sight. What is interesting is to look at the pump body with the gears removed (Figure 6). The right side of the pocket is the suction side of the pump. The left side of the pocket shows two separate pressure outlets. When these two circuits are traced, both circuits go to the primary pressure regulator valve in the valve body (Figure 7). It’s not until you examine this a bit more closely that you find one of the pressure supply circuits at the primary PR valve is used to provide main line pressure and converter supply oil while the other is used to operate the secondary pressure regulator valve (left valve line-up in Figure 8).

The secondary pressure regulator valve regulates both converter and lube pressure (see a partial hydraulic in Figure 9). It is an interesting way to provide the necessary volume and pressure required for both pulleys and the converter throughout various rpm driving conditions.

Figure 10 provides a full hydraulic schematic of the hydraulic system used in this K313 CVT. In next month’s issue of Transmission Digest, we will get inside the box to take a look at the pulleys.

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