Correct limitation of character acceleration

[native-engine]

How to limit the character acceleration without affecting the overall acceleration in order to correctly handle jumps and movements of the character on moving platforms such as a train? Here, when mixing accelerations, the speed is not limited, and it is incorrect to limit the overall acceleration:

// Calculate the speed of the character
m_characterVelocity = btVector3(0.0, 0.0, 0.0);

if (Controllers.Buttons[VK_W] || Controllers.Buttons[VK_S] || Controllers.Buttons[VK_A] || Controllers.Buttons[VK_D])
{
	if (Controllers.Buttons[VK_W]) m_characterVelocity += m_forwardDir * m_characterSpeed;
	if (Controllers.Buttons[VK_S]) m_characterVelocity -= m_forwardDir * m_characterSpeed;
	if (Controllers.Buttons[VK_A]) m_characterVelocity += m_strafeDir  * m_characterSpeed;
	if (Controllers.Buttons[VK_D]) m_characterVelocity -= m_strafeDir  * m_characterSpeed;

	if (m_characterVelocity.length() > m_characterSpeed) m_characterVelocity = m_characterVelocity.normalize() * m_characterSpeed;
}

// Adding the acceleration of the character to the forces acting on him
m_linearVelocity = threadData.m_characterCapsule->getLinearVelocity();
threadData.m_characterCapsule->setLinearVelocity(m_linearVelocity + m_characterVelocity);